Internal doors - ideally light weight with flat surfaces (Bilton HG1)

I'd welcome old internal doors, with flat and smooth hardboard or plywood surfaces. Handles and hinges would be removed. The doors will be placed over thick slabs of expanded polystyrene in a roof space. The slabs are supported underneath but if anyone walks on them, large pieces would break off around the edges. The doors will spread the weight of feet, like wearing large snow shoes. Collections from HG1 and HG2 areas preferred, for environmental reasons and minimise petrol consumption.