Two methods dominate debt payoff strategy. Both work. The difference is what they optimise for — and which one you'll actually stick to.
List all your debts by interest rate, highest to lowest. Pay the minimum on everything, then put every spare pound at the highest-rate debt. Once that's gone, move to the next highest. Repeat. Mathematically, this is the optimal approach — you pay the least total interest and clear debt in the shortest time.
List all your debts by balance, smallest to largest. Pay the minimum on everything, then put every spare pound at the smallest balance. Once that's gone, move to the next smallest. You'll pay more interest overall and the payoff period is longer — but you get early wins, which research shows is what keeps many people going.
If you've tried to pay off debt before and given up, use the snowball. If you've never had trouble staying committed to financial goals, use the avalanche. Either method beats the minimum payment approach by years.
If your highest-rate debt also happens to be your smallest balance, both methods are the same. If your highest-rate debt is a large mortgage and your smallest balance is a £300 store card, the snowball wins for motivation even if it costs slightly more.
Stop adding to the debt while you're paying it down. Carrying a balance on a credit card while putting spare money at another debt is like bailing out a boat without fixing the hole.