2000 MGF Intermittent Electronic Power Steering Fault

Hi,
Last year my MG's electronic power steering unit light came on and I had no power steering.
I took the car for a service, MOT & repair and the mechanic informed me that the EPSU would need to be replaced (a reconditioned unit was used). He did this and the electronic power steering came back on for a while. Unfortunately, the power steering light has now come back on and I again have no power steering. I took the car for an MOT today and asked them to look into the problem for me. They advised me that they had conducted a diagnostic on the unit but it is coming up with no faults! They removed the unit, cleaned it, replaced it and rebooted it but it still is not working. Obviously the car failed it's MOT and I now have a vehicle that cannot be used!
Can you please give me some advice as to what the problem is as I rely on the car daily and am stuck without it!
Kind Regards - Mick 137 aka - 4 wheels on a wagon but no way to drive it (legally)?