Loss of power when Hot

[LAN's GTI]

Was stuck in the mother of all traffic jams today, and although my temperature gauge stayed normal (It is working) My car was very down on power, to the point where I had to give it loads of revs to pull away. Stopped and opened the bonnet and the engine was cooking!

Got clear of traffic finally, and within 5 minutes the car was fine again, and was fine on the 50 mile drive home.

I know these cars do lose some power when hot, but have never experienced it this bad before,

Anyone think there may be a problem with it? Only had it serviced 2 months ago!