.... (I use the term travel in its most general sense: on a Friday evening in the UK you typically spend more time stationary than moving
)
The UK GCE exams cover just about the whole of May and June so some kind of overlap is unavoidable. I wanted to use the half term this year too but all dates were fully booked by mid September, as it was I had to wait for a cancellation for the June 12th date. Big venues are either stupidly expensive like the NEC / anything in London or book up a long time in advance.