I think that anything the tax man might be interested in if they decide to check you out (or the benefits office, or working tax credits or any of those things) they can demand to go back 7 years, and I think in some cases longer (I have read 20). So maybe it is worth at the least keeping all the statements of interest paid at the end of the tax year, pay slips etc, letters confirming payment schedules for benefits etc for at least 7 years, even if you don't keep all the intervening statements.
Also if you are in any form of shared accommodation/ blocks of flats/ move regularly I think it is worth keeping the utility bills etc from last address/ current addresses, so if someone does something cheeky like registering their bills in your name after you've left, you can prove you paid your bills regularly, and didn't run up a debt with the utility company (have read dreadful stories of people getting chased by bailiffs for money they didn't owe, and struggling to prove what actually happened when).
I keep the important documents for 10 years, in a box shoved in the back of a cupboard (not all the other bumpf you get from banks like "Dear Roseum, your overdraft has been approved for another year" or "we have dropped your interest rate to diddly squat"!
What about pension documents? MrNC has 10 different pensions, has had varied advice on consolidation, possibly was misadvised to take them out in the first place, and they all send bumf at least twice a year... and they keep changing their names!
Tax office just required me to send my P60s since 2008.
I keep old bank statements etc going back six years at least (and when I get my much-desired shredder , I'll get round to shredding the ones dating back 15 yrs!), although with the increase of online statements etc, I don't know how that will work?