I've just had a reply from the Department For Transport regarding banded steels:
Dear Mr Olsen,
Thank you for your enquiry regarding ‘banded’ wheels.
We are not aware of any regulations which forbid 'banded' road wheels.
However, you will still need to comply with all the relevant regulations, eg The Road Vehicles (Construction and Use) Regulations 1986 (C&U) as amended, and the Road Traffic Act 1988 (RTA) as amended. In particular, regulation 100 of C&U says "A motor vehicle, every trailer drawn thereby and all parts and accessories of such vehicle and trailer shall at all times be in such condition , ....... and the weight, distribution, packing and adjustment of the load of such vehicle or trailer shall at all times be such, that no danger is caused or is likely to be caused to any person in or on the vehicle or trailer or on a road."
Under Section 75 of the RTA it is an offence to supply a vehicle in an unroadworthy condition and under Section 76 of the RTA it is an offence to fit defective or unsuitable vehicle parts.
ISO standards exist for the design of passenger car road wheels (ISO 4000art 2 - 2007) and for testing (ISO 3006 – 2004 although this was under review). There is also a UNECE Regulation 124 which also sets out requirements for light vehicle wheels; i.e. http://www.unece.org/trans/main/wp29/wp29regs/r124e.pdf and that has also been amended recently although the attached link does not include the latest version as it will not come into force until approximately March 2011.
I have included the above because if trading standards test these wheels they are at liberty to choose any of the above.
The Department cannot give an authoritative interpretation of the law; that is a matter for the courts.
DfT – Transport Technology and Standards
Looks like they dont know either!