Flying within the country is no problem, freeze it and check the cooler as extra luggage....but going overseas is a whole nother ordeal. I have no idea. Federal regulations and such...Im pretty sure it is illegal to bring ANY food back with you from other countries into the USA...not sure on laws regarding leaving the USA with food or entering the UK with food.

If I were you I'd shoot some emails to the proper authorities both in the UK and USA to check legality.