Britain's sixth biggest mortgage provider, the bad bank running down the loans of collapsed UK lender Northern Rock, said it repaid 2.1 billion pounds ($3.4 billion) to the government last year after its annual profits more than doubled.

UK Asset Resolution (UKAR), which is running down the bad loans that were held by Northern Rock and other failed lender Bradford & Bingley, said on Friday its underlying 2011 profit was 1.09 billion pounds, up from 444 million in 2010, after a fall in losses on bad debts.

Britain should make a profit of 9-11 billion pounds on its bailout of Northern Rock, but may have to wait another 15 years to get all the cash, the body that oversees Britain's bank stakes said earlier this week.

($1 = 0.6266 British pounds)

(Reporting by Steve Slater; Editing by Mark Potter)