K reg ford fiesta losing power?

I have a K reg ford fiesta and today while driving on the motorway it seemed to lose power and started to judder. I pulled into the services checked the oil which was low so I topped up everything else seemed fine. I let it cool down a little and drove about another half an hour down the motorway and it did it again. The temperature seemed to go up a little bit but it wasn't overheating. I pulled over again and turned the engine off for half an hour. I drove the rest of the way home which was about another half an hour but kept the blowers on just in case it was heating up to quickly and it seemed to be fine. I'm taking it to the garage tomorrow but I just wondered if anyone could give me an idea if what it could be!

You are taking a K reg Fiesta to a garage? Their bill will probably be more than the car is worth.