Flexible Mortgages
The details will vary but basically this type of mortgage allows you to be flexible according to your future circumstances/ needs without having to pay a penalty.
So if you need to pay less due to unemployment or whatever, you can take a "payment holiday".
Or, if you win the lottery, you can pay more than usual - i.e. saving on interest payments in the long run.
There are many different versions of these mortgage and some will let you overpay the mortgage down to £1 and then borrow it back whenever you want to at the same rate as your mortgage.