This happened to me.
The nylon block the pedal hinges in is securred to the bulkead by an M6 nut on a stud and a locating pin that stick out of the back of the block.
Your pin has sheared off. About the only safe fix is a replacement block though you may get away with araldite or similar for a while.
They do come up on eBay every so often. Or you could get one machined up in aluminium.
Edit - Found a picture
http://www.ebay.com/itm/lancia-beta-throttle-pedal-bracket-/250988985876?ViewItem=&item=250988985876&nma=true&si=2JzH5Y8k4hsUDwV4BhinNPjv3pg%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557That one was sold by Chris Bastow ex of Betacar in Bradford - it might me worth asking him if he's got another.