can anybody please tell me the UK equivalent of a #4 washer, it doesnt exist here , rejetted my carbs to 40/ 147.5 running viper slip on and K&N lunchbox, looking to shim the needle but no luck with washers  

Can't say what english size you need really (#4 washer, dont you mean 4 inch or something?)
Can't you take out the needle, and take it to a hardware store or something? :p

And don't you have a clip by which you can set the needleheigth?

.125x.375x.040"

http://www.engineershandbook.com/Tables/washerdimensions.htm