Russian planes enter our airspace quite frequently too. http://www.bbc.co.uk/news/uk-scotland-highlands-islands-27157504
I love this bit from the article:
A spokesman said: "Russian military flights have never entered UK sovereign airspace without authorisation."
Except of course for when two Tu-160 Blackjack supersonic nuclear bombers made a mock attack run on Hull and the RAF never saw them until after they had turned for home
