This has happened to me 3 times over the years, most recently 8 weeks ago. The procedures at the GUM have changed a little since my previous last visit and it was a positive eye opener. For discretion I called a clinic 25 miles away and had a conversation with a doctor on what they call an Outreach programme (they do day clinics in local health centres in addition to the main hospital).
The conversation went along these lines;
Is there anything in particular makes you think you need testing?
Yes, the condom broke
Did it just split?
No the end came off (she had to squat down and fish it out with her fingers!)
Ok so there was contact
When did this happen?
Yesterday
It takes 2 weeks for the urine tests to show and 4 weeks for majority of blood tests to show, so we'll test you in 4 weeks time. (Syphilis takes 3 months to show)
Was it a regular partner?
No
A one-off?
Yes
Same sex or opposite sex?
Opposite
What ethnicity?
Asian
What were the circumstances?
Uhmm.....
I'm trying to establish the risk
She was an escort
Ok, was she a street worker or organised?
She was in an organised set-up
Ok, come in for a test in 4 weeks time, unless you show symptions in the meantime. But in my experience you have nothing to worry about. For these girls it's their livelihood, they are careful and are checked themselves regularly, probably much safer than a casual pick-up.
There were other questions about regular partner etc, but the commentary above is most salient to this forum and I certainly found it reassuring.
BTW I went for my checks 4 weeks later, got the all clear 11 days after that, then went and fucked the same girl 2 days later and told her I was clear!