I believe they are now are - well the chocolates but not the ice creams.That is what my brother in law told me the other day he is vegetarian and we were discussing it.
I know before May 2007 some were vegetarian and some were not and you had to look at the best before date and if it contained a letter think it was "u" they were suitable.
They changed where the chocolate came from I think.
Major companies, like Mars UK, take great care to provide accurate information about such matters (because the adverse publicity that would result from misleading information could cost them a lot of money).