Have just come back from the Newbury show. Bought some oven cleaning paste called Spruce. It is non acidic so has to be (gently) rubbed in then wiped straight off!. Its FAB!. Gets into all the corners of the trays, & takes stuff off that's been burnt on for months that I couldn't chip off with a blade!
I think they said would soon be in Lakeland, so keep your eyes open.