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Can't place the species, although from your size estimates it is quite a large one. Obviously an adult male (boxing-gloves on palps), and tip-toe stance indicates he is trying to take off for pastures new.
Now I've looked at your comments, it seems you already knew this! However, the silk is not "shot out", it is attached to the substrate (pic 2), then the spider dashes about and breaks the thread which floats aloft; more silk is released until it has enough bouyancy to lift the spider.
Lat/Lng: 52.5, -0.3
OS grid ref: TL1696