To quote from the original post, it must be awful to regret having sex, what must the woman be thinking?
I probably would not be sacked for having sex in my teabreak. Looking at my employee handbook under section 3, paragraph 11b, "The company policy allows any conduct, outside of work hours which is not(i) illegal, is not (ii) likely to bring the company in to direpute or and/or does not(iii)compromises its intellectual property rights".
Although there is no specific clause governing sexual congress, I would doubt that any liason would fall into any of these catergories in normal circumstances.