This is one of the bee mimics. I tend to missidentify them quite regularly. I'll go for Merodon equestris The Bulb Fly on this occasion. No doubt one of the real experts will point us both in the right direction.
Thanks for that. It will sound silly but while I was looking at it I did wonder if it was actually a bee because I couldn't see any antennae, but I just couldn't think of what it could be if it wasn't - it's just so fluffy! (the eyes should have been a give-away, I suppose, they are huge!). I've googled meredon equestris and there seem to be
some pictures which don't match so well (not enough yellow, too thin etc) but loads that really do.
This is Merodon equestris - as Lewis suggested. There's a loop in one of the wing veins that sets it apart from most other bee mimics. Hoverfly species that mimic bumblebees tend to have a variety of colour forms, so it's not a surprise that some images you find on google will match this specimen and others won't. It also looks like it's a newly emerged adult, the wings have not fully expanded and hardened yet!