Thanks for the responses guys
I left the car running and the fan looked ok, so I'm going to keep an eye on it. I'm still a little paranoid, but I'll see how it is over the next few days.
That's what puzzled me, how a part that important could be an advisory.
From the paperwork they did a 'health check' and the fan was mentioned when they were checking the coolant. But they did put the advisory on the MOT, they didn't call and the first I knew about it was when I went to collect the vehicle.
I reckon you're right there, they probalby noitced the fans when checking other things.
The last thing I want is damage to my engine
Cheers for the PM Zmanalex! if I need a replacement fan then I know who to go to