Exhaust emissions for UK MOT

Hi all,

This is a question for anyone in the UK really. My MX5 is about to go to its MOT. It's a 1991, and though it's got a cat, I'm pretty sure it got fried at one point since the last MOT. Does anyone know whether it's likely to pass the MOT emission test anyway? I remember reading that cars older than x years don't need a cat and are allowed to have higher emissions, but I can't remember what age that was. Am I imagining things or is this correct, and does anyone know since when cars have to have a cat?

Thanks

Eric