I spotted this on the floor on the bathroom, crawling along in a corner. I don't recognise it, and googling produced no immediate candidates. The body (including head) is about 8mm long. The thorax is bulbous, but pointed at the rear. It is pale yellow/brown with no obvious markings except a slightly darker narrow dorsal line running from the head to about halfway down its back. The segments of the legs are quite clear. The head features two very large black fangs(?). Although not aggressive it showed no great fear of me, and instead of panicking when captured like most spiders, it simply explored the edge of the glass in quite a methodical fashion, evidently looking for a gap.
You could well be right, thank you - sorry the photos weren't clearer. I've evicted this one; as I say, I haven't seen any others so I suppose it might have been a wandering stray. I see sac spiders can be biters, but I take it it's nothing to be too concerned about. I've been flat-sharing with false widows (s. grossa) for a while quite amicably and without incident, and I assume sac spiders are no more dangerous than them.