I was driving yesterday on the A1 upto Durham for my course and whilst doing about 65mph the emissions warning light came on (yellow).

The car is a Fabia Vrs. I pulled off the A1 to check things out but couldn't do anything. The car doesn't drive any differently, it doesn't use anymore diesel, it doesn't sound different and it still has all its performance.

Does anyone have any ideas as to why it has lit up? Could it just require re-setting or is something really amiss?

Take it you mean the exhaust system warning light? Had this happen to mine recently and turned out to be a failed temp sensory, fixed under warranty as I was drinking a coffee.

Yes thats the one.

What is that part then?

Sorry, don't know what the part was as done under warranty.