My engine fan has started to come on about 20-30 seconds after starting the engine,it does go off however after turning the ignition off. When it had its MOT last month(it passed with only tyre advisories) I got the mechanics to have a look and they plugged the diagnostic machine in and it came up with no faults, there are no lights on the dashboard...so any help with this will be appreciated

One fan only, low speed, and climate control in "Auto"? If so, then it's designed behaviour to ensure airflow over the air conditioning radiator.

Thanks KenoNeil for your reply, however having owned the car for 6 years it's never been on like it is now or made the noise that it's making so something is definitely wrong!

See, this is what happens when you don't give people relevant history!! ;-)

 

This could be the fan motor, but that needs a trained set of ears which aren't 500 miles away to confirm or discard.

Which fan is operating, the large or the small?

Sorry KenONeil I didn't know you wanted my life story! And shame on you for not hearing the noise 500 miles away lol.

The fan that is making the noise is the small 1 on the left hand side as you look under the bonnet.