This not so little guy has been in our Shed now for about a month. Same place at the back. Has moved if disturbed. He is quite big. Is it advisable to just leave him or her. Or could I find more of these popping up sometime if I do. Have slight phobia of bigger spiders such as our friend that I've called 'Sparky'. Could he bite ?
Difficult to ID from those pictures, it is most likely a house spider (Tegenaria species). They look intimidating due to their size, speed and habit of darting about, but they are in no way dangerous (nor is any UK spider).
It is very, very unlikely indeed that it will bite. Even if it did (you would have to grab hold of it & actively provoke it), it would be no worse than a pin prick, the venom has no perceivable effect on humans. They are harmless.
Would I be freaked out if I was surprised by one? Yes. But it wouldn't give me nightmares ;-)