Many thanks to Martin for the information

"DTC P1238 (Injector Malfunction) Probable cause is an injector mechanical malfunction or insufficient compression (valve etc) not an open or short malfunction of the ECM, EDU and injector circuit"

The vehicle came back in today for brakes and tyres, the owner was pleased that the MIL has stayed off. He also said the "bad egg" smell has now gone?

The fuel filter was replaced during the service and filled with diesel injector cleaner and one in the tank. The customer is off down the west country tomorrow so a long round trip, he will let me know next week if the MIL comes back on, if so looks like injectors out for testing and compression check

Thanks for all the help

Peter