There is an international phonetic alphabet, which is used in both countries. I haven't come across a writing system that's different. There is also an English biased phonetic alphabet, but I assume that if they use that at all in UK it would be the same, since it's made to make English speaking people happy (use y for y instead of j like the IPA does, etc.) It wouldn't be very helpful if I wrote stuff to you all in it if you don't know it though, because you wouldn't understand what I'm writing. Since we're only talking about a s/sh difference it isn't that hard to figure out from the way people are spelling things here. If we were talking about vowel differences that would be much more difficult.