I wonder if anyone has any idea how I can cure this problem.
The car seems to want to "cut out" or it "jerks". There is no particular time when it happens - either driving through the gears or just cruising along.
I've had my garage put it on the engine diagnostic computer, but no engine faults codes. It hasn't cut out......

 

I too have experienced the sudden hesitation or jerking as you describe. It has occurred since the car was new and no codes have been thrown so no repairs have been attempted. Mine usuallyy happens when accellerating in 1st or 2nd. I have always suspected the throttle-by-wire system but cannot prove it. However, I can overlook this occasional irritation because it has been an otherwise trouble-free car since the day I bought it.

 

Check the MAF sensor. Unplug the sensor right above the throttle body and see if it runs normal.