It is a bumble bee of sorts, I don't know the exact species.

try the Natural History Museum NaturePlus site http://www.nhm.ac.uk/natureplus/index.jspa

There's a bee identification section but you can also post photos (much as here) and get bug experts' help.

http://www.nhm.ac.uk/nature-online/life/insects-spiders/identification-guides-and-keys/bumblebees/index.html

I think it's a cuckoo bee, probably psithyrus campestris, and a female. Most of our bumble bees are white/buff/brown tailed and your picture shows a dark abdomen which fits with the cuckoo bee mum. Quite common, they use the nests of other bee species to lay their eggs, getting out of the rearing process. They don't do the pollen collecting bit. The shiny back is because they don't have so many hairs on their bums so the body plates show through the hairs.

Thanks all, as usual most helpful!
Bulba- I thought a bumble bee at first til I couldn't find one with a similar coloured abdomen.
Urbanite - I do use that site but their bee identification wasn't coming up with a match! I've tried to post pictures but even though I've joined I can't post and need some sort of numbers.
Worthy - I think you might just have got it! Cheers!