FEV would have had some influence too--it was spread into the atmosphere after the nuclear bombs dropped, and it seems likely to me that FEV could've been spread to other countries through the air--and possibly water contamination too. While the bulk of FEV would've been in the United States, I think one would see at least some minor FEV influence in the UK--such as animals mutated beyond what one would expect from a "normal" nuclear fallout.