A male bee fly, Bombylius major (Diptera: Bombyliidae). The proboscis is not usually forked like this. I thought the tip might have got damaged when I caught it but maybe not: there are other examples out on the web, for instance here. Here is a close-up of the proboscis:
This image also shows the narrow gap between the eyes on the top of the head, which is charcteristic of the males in this species.
This image also shows the pattern of markings on the wings that distinguishes B. major from other Bombylius species:
Specimen caught on the dam at the lower end of the large lake, Whiteknights Park, Reading, UK, on 2014-03-23.