Forget any of those expensive specialist oven cleaning products. All you need is some steam, some lemon juice and possibly some brilliantly cheap bicarbonate of soda.
Turn on the oven for 20 minutes to get it to top temperature. Get an ovenproof bowl, squeeze in the juice of half a lemon and boil the kettle. When the oven's hot, turn it off. Pour the boiling water in with the lemon juice, put it in the oven and leave it to steam for half an hour. Use a damp cloth to wipe the oven as clean as you can. Use a metal scourer on areas that need extra muscle. If it's really encrusted, mix two teaspoons of bicarbonate with the juice from the other half of the lemon, apply, leave for a few minutes, then scrub. Make sure you remove all the bicard residue with a damp cloth or it will leave white streaks. Buff up with a cloth and your oven will sparkle like new.
To make cleaning even easier, stick a bowl of boiling water in the oven after each use - or at least after each time you've roasted some meat. The steam will prevent the oil and residue from setting hard. Just leave the bowl in the oven until it's cooled, take it out, give the surfaces a quick wipe with a damp cloth and then buff it dry.
Joanna Gosling is the author of Simply Wonderwoman, www.kylebooks.com