Are composite fuel tanks legal for road use?

I ask because I saw a nice build thread on another forum where a composite fuel tank was made up for a bike it looked smart and was also an interesting shape. this got me thinking it could be a good way to build a new tank for my car. It could have a fairly complex shape so that its fits in and still had a decent capacity. So is it legal?

i guess it would be treated as plastic, which can be used, as long as its got certification to say it meets all sorts of safety requirements, details in the IVA manual link below

metal (aluminium or even steel if you don't mind the weight) don't need any of this, so much easier to make legal

as this is post IVA/SVA would it fail an MOT?

Only fail points relating to fuel system on the MoT is insecure components, cracked or chaffed hoses or leaking system.

[Edited on 12/3/12 by loggyboy]