30 weeks in total - 10 weeks per term.
First year exams typically weeks 6-8; second year exams typically weeks 7-9, third and fourth year exams typically 5-7.
But if you do a second year module in year 1 or 3 then expect a few days where everyone else is free.
As for 30 week years - Oxbridge have 24 or something, others have 28 or so but they end as soon as exams finish and results are given during the holidays. Warwick give results in week 10, term 3. Warwick have quite long terms and start and finish later. By the time you go up, many others would have been at uni for 3 weeks.