It's always a difficult one this, as generally the success of a good manufactured spending route is dependent on it staying secret and so only being used by a few people. Here's a starter option though, that I've used to good effect when I'm a few hundred pounds short of my spend target. Load an Oyster card with £90 (the maximum, plus there's the £5 spend for the card deposit). Ask for a refund. They will refund it, but only to a card. Just pop in your debit card when prompted, and there you have it. £95 flipped from your credit card into your debit card account.