If I remember correctly,the only function of plastic capping is to protect the cables while the wall is being plastered,as I,m sure we all know how good plasterers are at slicing into cables,and even metal capping would not prevent damage from a drill or nail.I dont recall there being anything in the regs to say that capping is a must,although I stand to be corrected on this point.The first Wylex RCD boards had a combined RCD/main switch and were a pain if you got a fault,however at least they provided protection.At one point I had a brief stint as a QM for a firm of house bashers and the gaffer was so tight he used Hager boards with cartridge fuses and fitted one RCD socket in the hall,this was when you only needed RCD protection on sockets that may be used for equipment used outdoors,in fact he even had the sockets labelled up to state this.I left the company following an argument over my testing of new works,I wanted to do proper tests and he just wanted me to dream up numbers for the results.