PEP (the post exposure prophylaxis drug for HIV) is available in the UK under certain conditions - for example if you have sex with someone who then discovers they are HIV positive, or if you have unprotected sex with someone from an area known to be high risk for HIV. I'm guessing you could lie about this and get the drug, or find some other way of getting PEP.
H O W E V E R ........
The side effects of these drugs are truly horrendous. I'd think any WG taking them after possible exposure would be unfit to work for the duration of treatment , due to the side effects.
A pretty bad idea.