This is a swarm of honey bees. You can see how they hang in a cluster from the branch of a tree, with thousands of bees in a swarm. They are usually very docile and not considered dangerous if left alone.
Bumble bees are larger, rounder and more hairy than honey bees. There are only a few hundred in a colony; often they nest in bird boxes, compost heaps and holes in the ground. Native or common bumblebees have tails that are white, red, buff or brown. As the bee gets older, some colours may fade, so ‘red’ tails may begin to appear buff or orange in late summer. There can be variation in the number, colour and position of bands, depending on the species of bumblebee, but a typical pattern consists of two yellow bands: one on the thorax, and one on the abdomen. The hair on the bumblebee’s head is black.
There are about 250 species of solitary bee in Britain. They are generally smaller than bumble bees and quite furry, and they do not live in colonies. The Wildlife Trusts have produced some useful information on Solitary Bees on their website.
If it is yellow and black with thin wings it is a wasp (or, if quite large, possibly a hornet)