There is only a trickle of cold water coming out of the cold tap in the kitchen the pipe is blocked took the stopcock off and it has disintegrated and think the fiber washer fell into pipe?

Sounds as though you have galvanised piping. Your only solution there is to take the section of piping out and inspect it at the next joint and see whether the condition of the piping is adequate. If not take out the next section of piping until you find that the piping is in better condition. My recommendation is to replace with copper, for two reasons, copper does not corrode and is easy to install. Would be advisable to replace the stopcock and even in some cases the tap as well.