Various different car makers in the 80s stamped the key No on the boot/tailgate lock, but you need to be able to open the tailgate and remove the lock to find it! however your problem is that you cant get a new key until Tuesday, £120 in fines before you start!
Assuming that you can get into the car, see if you can borrow a slide hammer, from a garage, with a self tapper atatchment, screw it into the ignition and knock the locking barrel out, this will ruin it by the way, car can then be started with a flat blade screwdriver.. unless it has an immobilizer, in which case just get the car recovered, and have a new lock set fitted, not that exceptive, and around an hour of labour, double check that you haven't locked the keys in the car!!!
cant really suggest much else
Good luck!
Tom