Fuel tank comprising an urea tank

A multi compartment vessel for fixing to a vehicle, the vessel including a fuel tank (32) formed of moulded plastic in which a wall (11b,11c) of the fuel tank comprises a concavity (11a) which defines the volume of a urea storage tank (11) for storing for use in a vehicle engine exhaust treatment system. The vessel has a closure element (50) over the concavity and the urea tank (11) is completely surrounded by a fuel in the fuel tank (32) to obtain the maximum insulating effect from the fuel. The vessel may be formed by a rotational moulding process.