You can take the 25% and leave the rest to carry on accumulating. It's only if you buy an annuity or similar that triggers monthly fixed payments. Gideon removed the whole annuity racket allowing pensioners the option to pick what they felt was the best option.
Interesting, but doesn't taking the 25% out tax free trigger the start of the pension payments?
(Not really relevant in my current situation as I should have my mortgage paid off by the time I'm 52.)