A BARRIER FIELD OF THE INVENTION The present invention relates to a barrier assembled from a number of panels that are 5 interlocked around posts to form the barrier. BACKGROUND TO THE INVENTION Barriers, such as walls or fences, can be formed from a number of panels that are aligned together and supported in place by posts that are dispersed between the panels. 10 They are typically formed by securing the posts in place at periodic intervals and then attaching or connecting panels between the posts to form the barrier. The panels are attached to the posts by a suitable affixing means. SUMMARY OF THE INVENTION 15 An object of the present invemion is to provide alternative means for supporting and interlocking panels when erecting a barrier, and/or components for erecting a barrier. Described herein is a barrier assembly comprising at least two panels and at least one post, wherein each panel comprises a rebate along at least part of the length of at least one edge, the rebate extending inwards from the edge between the opposing faces of the panel such that when the 20 edge is arranged adjacent a corresponding edge of another panel the combination of the rebates form an aperture for receiving a post, the aperture not being visible when the panels are viewed face on, and wherein the post is positioned in the aperture to support the corresponding panels. Once assembled, the posts are not visible when the panels are viewed face-on. As described herein the barrier assembly comprises more than two panels assembled with a 25 requisite number of posts. As described herein the panels and/or post can be secured to the ground with cement or other suitable adhesive. As described herein each panel is a composite formed from a plurality of layers. In one aspect the present invention may be said to consist in a panel for assembling in 30 conjunction with at least one supporting post, the panel comprising: a cover layer applied to a substrate to form a panel, the cover layer comprising fabric and resin, and a rebate along at least part of the length of at least one edge, the rebate extending inwards from the edge between the opposing faces of the panel such that when the edge is arranged adjacent a corresponding edge of another panel the combination of the rebates forms an aperture for supporting a post, the aperture 35 not being visible when the panels are viewed face on. In another aspect the present invention may be said to consist in a method of constructing a panel comprising: forming a rebate along at least part of the length of at least one substrate edge - 1between opposing faces of the substrate, applying a resin to at least one face of the substrate, applying a fabric layer to the resin to produce a bonded cover layer on the substrate, the substrate and cover layer forming a panel, wherein the rebate extends inwards from the edge between the opposing faces of the panel such that when the edge is arranged adjacent a corresponding edge of 5 another panel the combination of the rebates form an aperture fOT supporting a post, the aperture not being visible when the panels are viewed face on. In another aspect, the present invention may be said to consist in a set of one or more panels as described above and posts that can be assembled to form a barrier assembly. In another aspect the present invention may be said to consist in a method for assembling a 10 barrier comprising erecting two or more panels as described above by erecting one or more posts and arranging each panel such that a rebate along one edge engages with a respective post. In another aspect the present invention may be said to consist in a barrier comprising two or more panels supported by one or more posts, the posts residing within outer faces of the panels in apertures formed from rebates in adjacent panels. 15 As described herein the skin comprises a fabric layer and a Fin sh layer bonded with resin. In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of 20 information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art. The term "comprising" as used in this specification means "consisting at least in part of'. Related terms such as "comprise" and "comprised" are to be interpreted in the same manner. To those skilled in the art to which the invention relates, many changes in construction 25 and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the invention as defined in the appended claims. The disclosures and the descriptions herein are purely illustrative and are not intended to be in any sense limiting. BRIEF DESCRIPTION OF THE DRAWINGS 30 Preferred embodiments of the invention will be described with reference to the following drawings of which: Figure l a shows a plan view of a panel for a barrier in accordance with the present inVention, Figure lb shows a elevation view of a post in accordance with the present invention, 35 Figure 2 shows plan and elevation views of three panels arranged adjacently, and -2- DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The present invention relates to panels I and posts 2 that call be assembled to form a barrier 3. It also relates to the barrier itself, and also a method of assembling posts and panels in order to form a barrier. 5 Figure Ia shows in plan one embodiment of a panel 1 used in the present invention. A number of such panels can assembled to form a barrier 3 in a modular fashion. The barrier could be a fence, wall, planter box or similar. The panel 1 is formed as a composite sandwich panel comprising a polystyrene (or similar) core 15. Two laminated outer skins 5a, 5b of reinforcement are provided to give a self supporting strong durable panel. The outer skins S, Sb comprise a resin 10 16 is applied to both sides of the core 15. the resin preferably being a polyurethane adhesive such as SIKAFORCE - 7718L30, or any other suitable resin for strength and bonding. The skins further comprise a polyester fabric layer 17 is placed over the resin layer 16 on both sides and attached to the core 15. They further comprise a second resin layer 18 (again polyurethane or other suitable adhesive) is placed over both fabric layers 17. The skins also comprise a sand coating 19 is placed 15 on both sides, adhered in place by the resin layer 18. An acrylic or other patent can be applied to provide and attractive finish. Various other cosmetic finishes are available to provide an attractive front and back surface, using different chip, resin and paint coatings incorporated at the manufacturing stage. The panel is square or preferably rectangular in shape and can come in any suitable size, for example 2 metres (height) x 1.8 mettes (width). The panel can have any suitable 20 thickness, such as 100mm. This comprises a 53 mm thick rebate, 98mm thick core, and outer skins Sa, 5b of 1mm thick each. These dimensions are exemplary only, and the panel could be formed with other suitable dimensions. The height relates to the length of the side of the panel in the vertical direction when it is installed in a vertical manner, and the width relates to the lateral distance from edge to edge 7. In Figure 1, only a portion of the width of the panel 1 is shown, to indicate 25 that any width is possible. A rebate or recess 7 is formed along one and preferably both vertical edges of the panel 1. The rebate is formed by hot wire cutting or otherwise cutting the polystyrene core 15 to form an opening that extends inwardly into the panel 1 and sits between the two outer faces Sa, 5b. Prefctably, the rebate 7 extends the entire height of the panel along the vertical edge 8, although this 30 is not essential. A folded galvanised steel insert 20 is placed in each rebate 7. The panel is manufactured in the following manner. The polystyrene core 15 is prepared and then the rebate formed in one or more edges. Inserts 20 are fitted into the rebates, and a first resin mix is prepared and applied to both sides of the core 15 to provide the first resin layer 16. The fabric 17 is applied to both sides and then a second resin mix prepared, and applied to the fabric to 35 provide the second resin layers 18. The sand 19 or other finish is applied, and then a paint finish is applied. -3- The rebate is dimensioned to have a depth "d" and a thickness "t" such that it can receive one half of a supporting post 2. Referring to Figure 1 b, preferably the post is an elongate member with a rectangular or square cross-section, formed from galvanised pre-fabricated pre-drilled steel. The post has a height "h" preferably similar in height to the panel 1. The post has a number of pre 5 drilled holes 22a to 22c, for securing the panels to the post via screws. The rebate is shaped to snugly fit the shape of the cross-section of the post. Preferably, the post has a 50mm x 50mm cross-section, although this is not essential. It could be rectangular in cross-section or be square and have other dimensions. A plastic cap 23 is placed over the post 2. Figure 2 shows in plan and elevation view of three interconnected panels Ia, 1b, 1c to form 10 a barrier. Each panel has at least one rebate like that in Figure 1. The first panel lb comprises rebates 7 on either edge 8 which match corresponding rebates in the corresponding edges 8 of panel la and 1c. When the panels la-1c are arranged such that the edges 8 with the rebates 7 are abutted together, the combination of the corresponding rebates 7 forms an aperture 10 extending along the length of the abutting edges. An aperture 10 is shown in Figure 2, formed from the rebates 7 of 15 panels Ia, l b abutted together. This aperture is formed in a manner to receive a post 2. When the barrier is erected, a post resides in each of the apertures to support and interlock the panels to form the barrier a post 2. The elevation view in Figure 2 shows in dotted lines the positioning of the aperture 10 and posts 2 in relation to the edges 8 of each panel la-1c. 'The posts 2 are secured by cement 26 or other filler in a suitable size holed 25 in the ground. Any suitable number of the panels 20 can be arranged in an abutting fashion to provide a barrier of the desired length. The panels residing at each end of the barrier might only have their internal edge comprising a rebate, and have a normal flush finish on their external edge to provide for a more attractive finish. Figure 3 shows in perspective view an example of an erected barrier using the components of the system. The figure shows panels 1b and 1c erected and held in place with a post 2. A third 25 barrier Ia is shown being assembled to the barrier 3 with another post 2. The post 2 sits within the aperture 10 and is secured in place by cement or other adhesive to retain the panels Ih, 1c in place. Referring to Figures 2 and 3, the barrier can be erected in the following manner. Levels are established along with post positions. The footings (holes 25) are then prepared for the posts (the holes 25 are not shown in Figure 3 for clarity). The first post 2 is then cemented 26 in place in the 30 first hole 25. The panel 1c is then aligned with die post and secured in place using screws that attached into the panel 1c and the pre-drilled holes 22a-22c in the post 2. The panel Ic can be aligned with the holes 2 2 a- 2 2 c on the post 2 using a locator jig 27 (visible in Figure 1 b). This assists in holding the panel Ic in place. Once the panel is in place, the next post 2 is aligned and cemented in place, and another panel attached. This process is repeated until all panels e.g. 1 a to I c and all 35 posts 2 ate in place to provide the desired length of barrier. Once in place the posts are not visible -4when viewing the battier from the front or back faces of the panels ia, 1b, Ic. Touch up paint work can then be done. It will be appreciated that the posts could all be secured in place first and the panels then interlocked with the posts, or alternatively the panels could be positioned first and then the posts 5 slotted into the formed apertures. Other possible methods of erection of the barrier are also possible. Once or as the barrier is erected, it is possible to place a top capping 28 (of which a portion is shown in Figure 3) to obscure the posts. The capping is formed of folded galvanised steel. Alternatively, the capping might comprise mixing a resin and applying it to the top of the posts, 10 applying sand coating and the painting to obscure the posts. Alternatively, the recesses/rebates 7 might not extend fully along the edges 8 such that the aperture 10 is not visible from the top of the panels la-1c once assembled. In this case the posts would be slightly smaller in height than the panels so they do not sit fldsh with the top surface. In a preferred embodiment the recess 7 is rectangular or square, although this is not 15 essentiaL Other shaped rebates would be possible, where they correspond with other shaped posts. For example round or polyhedral cross-section posts are possible. The figures show small gaps between adjacent panels. This is not necessary, and the panels should be arranged as flush as possible, In practice, some small gap may occur, however. The modular system provides a barrier constructed in a modular fashion form panels and 20 posts without posts being visible. The post can be used as both a support and a joiner. -5-