Hello, I hope the following assists you.
From the description you've given and the fact the garage suspected a badly fitted fuel filter there is likely to be a fuel pressure concern.
The reason for this can be a fuel filter blockage but it can also range from an air leak into the fuel system to a failing injector or fuel pump.
To check the fuel system requires specialist equipment so the fuel pressure can be checked with the engine running, this is measured electronically due to the extreme pressures involved, at the same time the amount of fuel returned from each injector is measured, this helps to pinpoint if an injector is faulty and which one is.
As the engine warning was displayed then a fault code will have been stored in the engine management memory, the memory needs to be read to obtain the fault code, this will confirm if it is a fuel pressure concern. Any garage can check the memory so the cost is minimal even fast fit firms such as Quick Fit are equipped to do this.
With regard to the traction control/ESP lamp don't worry about this you'll find when the engine management fault is repaired the light won't come on, this only comes on as the engine management is part of the traction control system and as the traction control has been made aware there is an engine management fault it can't operate correctly so illuminates the warning light.
I hope this helps but if you have more questions regarding this let me know and I'll reply as soon as I'm able to.
Thanks for your prompt reply, Sean. I don't really rate my local Ford garage, but is this the sort of thing I really need to go to them for?
to start with you need the fault code(s) that are stored, any garage can retrieve these, as I said earlier even your local quick fit can do a quick diagnostic scan, this will at least confirm if it is a fuel concern that is causing the problem so to start with you don't need to go to a Ford dealer. There are many good independent garages now who are more than capable of diagnosing this without the costs associated with main dealers.
You can ask around as word of mouth tends to be a good guide to finding a reliable local garage or choose a garage that is a member of the RMI.
Let me know if I can assist further.