So if you put the £ symbol in chat followed by some numbers it will either display nothing (just the £ but it appears to be bolded) or a different symbol (eg, a square).
It looks as though £ strips off the last 2 digits from the following string, so £1000 gets posted in chat as £10.
The € has a similar issue but it strips off the last 4 digits (€10000 gets posted as €1).
!"$^&*() all work fine, as do @~’#<>?,./|\
So the only problem characters on the standard UK keyboard are £ and €.