This light came on after about 150 miles on a trip yesterday - car performed fine and I did a round trip of about 350 miles. Light only went out for a brief period after I refuelled. What are the causes of the light coming on?

 

We'll know once you get the code read and report back. Otherwise it's all a pointless guess. In the US parts places will read OBDii codes for you.

 

OP in Bedfordshire, probably a bit of a trip to get Autozone to check it for him.
PeteCB, check out eBay for a Bluetooth OBD2 reader, you can get them for anywhere between £4 & 50. Mine came with full versions of both Torque and Dash Commander. You can read all the generic codes, reset them, PLUS get a crap-ton of real-time information.