Welcome back to the forum.
The chance any particular woman residing in the UK has HIV is near zero, assuming she is not an immigrant from an HIV-endemic area like southern Africa. Last I heard, your Health Protection Agency (HPA, UK's equivalent to CDC in the US) estimated that fewer than 1 in 1,000 sexually active women have HIV. This is true even for women who are commercial sex workers.
Second, sexual transmission of HIV generally requires unprotected insertion of a penis into a vagina, rectum, or mouth. Failure of attempted penetration means there was no measurable risk of HIV transmission, even in the unlikely event your partner was infected. That your penis "might have come in contact with her vaginal fluid" makes no difference.
Here is a thread that discusses tSTD/HIV transmission in detail, explaining scientifically why exposures like this carry little or no risk. You should find it reassuring. Start reading with the folllow-up comments that start December 14:
http://www.medhelp.org/posts/show/1119533
For those reasons, you do not need HIV testing and should simply forget this episode in relation to HIV risk.
Regards-- HHH, MD