Yes, this is absolutely my own experience too (and not just in the UK). There's a lot of damaged souls out there, and they congregate around dating sites. In fact I've even come to conclude that there is a species of bitter woman who specifically joins such sites with a preplanned intention of revenging on men by generally messing them around.
Just think about it: just why would a woman join a dating site? Men and women's motives are somewhat different here I'd say. Men are still expected to do the running when it comes to selecting a mate - and hence they get involved in dating sites when the pool of available women has dried up - or perhaps because they are too shy(or burned) to make approaches in public arenas. But as for women - the same motives can hardly be paramount. All but the most revolting of women can fail to get approached by men (in the `real` off-line world) if she puts herself out there. so 'd suggest that the ones who go on dating sites are doing so in order that they can more easily screen out the applicants (as it were) - and possibly because they have a very exacting ideal as to exactly what type of man their partner should be.Or..for reasons suggested above.
If you are looking for a partner, then I've concluded that the best (and possibly only) way to do this is to pursue your own `leisure interests` with abandon...and maybe, just maybe,you'll come across a woman who shares the same interest (who also will be seeing you at your best) and something will spark off that way.