Do a search at SamKnows click here to see if you can get O2 BB click here, which starts at £12.23 for a 8 meg connection.
If yes, go via a cashback site click here / click here to get some money back.
If you own an O2 mobile (contract/PAYG) you can get a further £5 off your bill each month. A PAYG O2 phone will require a minimum of £10 topup every quarter to maintain the £20 (over a quarter) discount. G