Any ideas what this is ? looks aftermarket mod but im not sure not up on VWs is under the clutch pedal

That`s the "brake/clutch pedal "stop plate".   Keeps pedals upright. Looks to be a cobbled job but as long as it buts up against the pedal assembly correctly it will be fine  Take a look thro`my build thread... "Birth of a Buggy" and I will have some photo`s on there.

As Paul says it's to stop the brake and clutch pedals flopping backwards and to enable adjustment to get the pedal position correct.

Cheers 🍻

Better guys  try and not lose it then , hopefully not too far off staring to clean up pedal assembly