Following on from the recommendation of a friend, I recently ordered the Silverwood multisize cake tin from Lakeland [along with a few other goodies ;)]. I wasn't convinced that it would fit in my oven as the shelves are exactly 12" deep, leaving hardly any room for the door to close. But since it was free delivery [those 'other' goodies took me over £50... eeek!] and free returns, there was no harm in trying.
The tin is designed to be fully collapsible which allows it to be stored flat. It arrived in 7 pieces; a solid base tray, four sides which interlink with each other and two dividers which allow you to make up to four cakes at once.
When constructed, it is a 12" square and the sides simply sit on top of the base tray.