If it were here in the U.S, it'd deffinitely be a wasp nest, alternately called yellow jackets or hornets. They're pretty aggressive when agitated and your probably fortunate you weren't stung. I keep honey bees and have been stung several times... so much so that it's painless now (and no arthritis symptoms) but one sting by a wasp produces an entirely different result.
If it's available in the U.K, a product named
Raid Wasp and Hornet Spray (seen here:
http://www.scotts.com...ller-20120501&sissr=1 ) works very well. If you use it, spray the entire nest thoroughly at least twice.
Bees don't nest in trees... especially honey bees. There are some ground nesting bees...