Because you just can't get a good cup of Earl Gray in orbit.  </rimshot>

Actually they voted in 1986 to not participate in human space missions.  Sensible and boring...oh wait this is England so that makes sense.

http://www.thespacereview.com/article/1084/1

The article's lede is that Britain might be returning to the human spaceflight arena.  But if you read through the whole article you will see it is merely an opinion piece without any basis in fact.

Looking at a search on the subject, it appears people bemoan the current status of the lack of Englishmen in space every couple of years.

Oh well, space free of Englishmen...I guess we'll all keep drinking our squeeze tubes of coffee.