Please read my comment, dated today in follow-up to a question asked a couple of days ago: http://www.medhelp.org/posts/show/326593. The
prevalence of HIV in the general population in the UK probably is simlar to the US; if anything, probably it is lower. (However, there are proportionately more immigrants from HIV-endemic counries in the UK than in the US, but that doesn't influence your situation unless either of your partners was from such a country.)
You describe a low risk situation, if your partners were not at obvious high risk; and even if they were, the chance you were infected was low. As I have stated innumerable times--please take the time to read almost any 10 threads at random--your symptoms are meaningless in relation to the possiblity you have HIV.
From a medical or risk assessment perspective, you don't need HIV testing at all on account of these events. But if you do it, the timing is up to you. There is no point in testing before around 4 weeks after the last sex either of the women you are concerned about. If you do it then, the negative result--which is what you can expect--will be very reassuring but not definitive, and your anxieties undoubtedly will lead you to have another test later. If your mental state can handle the additional delay, just have a single test 6-8 weeks after the last exposure.
Better yet, visit one of your country's excellent GUM clinics and follow their advice. You will find them equally reassuring as my advice and their testing recommendations similar, except for the possibility that they will conservatively recommend waiting as long as 3 months for a definitive test result.
In the meantime, relax. The odds really are overwhelmingly in your favor.
Best wishes-- HHH, MD