There’s a lot of rubbish being posted on this thread.
1) Take the longest term possible. If you need a lower mortgage payment using a longer term because you’ve changed to a lower paid job or your other half is on maternity pay, the bank aren’t likely to bend over backwards to help, so take the longer term whilst they’re offering it.
2) Over pay as if you’re on a shorter term. The 10% overpayment you’re allowed is 10% of the balance of the loan – ie, if you take a 150k mortgage, you can pay off £15K or so in overpayments in the first year.
3) Fixes cost more for a longer fix. As others have said, view a fix like an insurance policy. Again, think about if you’ll have kids or want to get a job that’s less aggro and less money.
4) Overpay. Overpay. Overpay. If you overpay, most lenders will not shorten the term of the loan unless you ask. So if you need to stop overpaying, you’ll have the benefit of a lower payment than you would have had if you’d never overpaid at all.
5) Have I mentioned overpaying?