This is the Common Bee Fly, Bombylius major. This is a common and widespread species of fly usually seen during April and May. They are associated parasites of solitary bees and can often be seen hovering over the nesting aggregations of solitary bees where the female fly scatters her eggs.
Although the proboscis looks a little intimidating it is used to nectar from long tubed spring flowers only and the fly is harmless. They are often described as being a cross between a bee and a mosquito.