The 'check engine light' in the centre of the dash on my P1 came on today. The manual says to stop and turn the motor off then restart it and the light should go out which it did. Howvever the light came back on about 20 miles later. Did the same and it has not come on since.

What is this light for and what exactly is it refering to in the motor?

Spoke to the dealer who said pop it in and we will sort it its a very quick job we'll do it while you wait.

 

CEL is telling you the ECU has found a fault and stores a code of what the fault is.
If you take it to a Subaru dealer, they will tell you what the code is. Might be something wrong or might just be something that needs cleaning, but never ingnore CEL.
Cheers.
Ian.