You’re right - the fault came back and I have since topped up with BP fuel and added a bottle of STP injectors cleaner (the once every 3,000 miles version) into the tank and taken it for a quick blast on the motorway at 3,500 revs. Light still on when I parked but will watch what happens over the next week or so. If still there, will take it back to the garage as they said they would sort it.