If you are talking about the series I think you are then it is the BRSCC Lumination road saloon series that you watched at Anglesey. This has cars up to 2 litre multi valve, and up to 1.8 litre 8 valve, with modified engines, and 2 or 3 classes for standard engined cars. All cars have to have the interior and an MOT, and driven and hopefully from the circuit. The engines in the modified cars have to look standard from the outside but anything goes in them. The web site is:
http://www.roadsaloons.com/Home.htm
THe other series is run by the BARC/BRSCC and is the super road/ modified production saloon series. This allows the interiors to be removed and alot more to the engine. try:
www.rscc.co.uk for more info.
Both series have been very successfull in the past but not so in recent years. The 750mc series have pretty much taken over the budget saloon car series.