Accelerator pedal stuck down

C3 VT 1.1 59 plate
My wife recently had the accelerator pedal on her C3 stick in the fully down position.
She was at slow speed entering a island and was able to pull in safely, with the Revs HIGH. She turned ignition off and had to lift the pedal back up manually.
There were/are NO issues with carpets.
She drove home with no problems; the car has been diagnosed as "clear" by a local Independent Garage -- although a Clutch issue was observed (related ?)
I've been persuaded by local Citroen Dealer to have diagnostic check done by them - this Thursday.
Anyone had anything similar ?

My thoughts would be in this case, don't bother with more diagnostics, put the money towards a new accelerator pedal.

The pedal is a controller, in the sense that all it does is generate electrical signals which are passed on via wiring. I think it's highly unlikely that diagnosis will show anything conclusive for what sounds like a physical problem.

My worry would be that having stuck once for no apparent external reason the problem could re-occur. It doesn't sound likely that a return spring has broken or come adrift as the pedal is working at the moment.

Thanks for your thoughts "Missing Lincs".
The local garage (who I have faith in) also did a good physical examination and could find no obvious problem.
Forgive my ignorance but, could the Citroen garage's diagnostic check detect IF the pedal electrics was faulty?

Any garage or mechanic with suitable test equipment can detect faulty electrics in the accelerator pedal.

There's also a good chance that the car would show a warning light or possibly go into 'limp' mode with a throttle pedal electrical fault.

Essentially the throttle pedal is a position sensor. It does this using two sensor circuits, the car's ECU looks at the two readings and if they are different, which would be the case if one was faulty, it flags an error and if appropriate will take action.

Nothing in the sensor circuits would make the pedal stick down.

... hence your comment that it must be a mechanical issue ?
No warning lights were evident - My wife remembers looking for One !
So would a completely new unit solve issue OR a removal, general tidy up and replacement of original unit be favourite ?
I've driven for last two days (100 miles) with no repeat.
I'll let you know what the Dealer Advice is !
Thanks
Mike