It is a bee-fly, Bombylius sp., and they are harmless to humans (the pointy thing on the front is a proboscis not a stinger).
Here's an excellent introduction to bee-flies (there are nine species in Britain)
The Bee-fly is amazing. It makes you wonder about its evolution. Was it originally a bee that became a fly or a fly that 'looked' at a bee, and understanding that bees had 'stinging power' decided - "Yep! I think I'll dress up like one of those powerful creatures so that my predators will think twice about eating me"...
It's a 'Hoverfly' as well isn't it?
Mimicry can be fascinating and confusing. There is much we can observe (and the more we look, the more we see), but that often throws up more questions than answers.
Bee-flies are not actually that closely related to hover flies. Yes, they are both flies (DIptera), abd they are both in the suborder Brachycera (http://en.wikipedia.org/wiki/Brachycera). But that is a fair way up from their particular familes (bee-flies are in the Bombyliidae, hover flies are in the Syrphidae).
There are much more-unrealted species that have come to look similar.
'Convergent evolution' is where different creatures come to look similar because they occupy similar niches. And when that happens, it can appear that one creature is mimicing another one, apparently to gain some protection (a hover fly looking like a wasp, perhaps). That may be true, but there are probably greater subtleties than we appreciate.