This has been seen many times before, and there is a FAQ thread in the Leon Mk.1 section about it.
http://www.seatcupra.net/forums/showthread.php?t=202318
The little box on the pedal that the master cylinder push-rod goes into is only spot-welded and fails after a while. It's a clutch-pedal-out job, and the hardest part is working in the footwell - there's not a lot of room. You can weld up the box yourself if you are equipped, or get a new pedal.
Check to see if the master-cylinder push-rod is still straight and that the seals are good. The pushrod snaps back against the end of the master cylinder when this happens, and can damage the seals. Hydraulic fluid then leaks under the carpet so you can't see it - but the reservoir slowly empties.