In my own lifetime, I've seen two changes to British culture which I attribute to immigration:
* Immigrants from India have improved our cooking skills
* Immigrants from the West Indies (Caribbean islands like Jamaica) have made us sexier (Salsa dancing (like ballroom dancing, but sexier) from South America helps with this as well)
However - now that we know that the best flirting technique is to make the girls laugh (
link), it's advantage Englishmen! Having a delicious sense of humour is part of the male culture here. Most girls from most countries will melt when you make them laugh.