Unfortunately for me, the players don't understand sliding block puzzles. The Alfa is now blocked in by a very sloppily-parked car (though credit where it's due, for that car to end up where it did took some well-judged driving).
Hang on... the car that was completely blocking the Alfa in has now gone elsewhere, leaving a precisely Alfa-sized gap between the remaining cars. Which is good, except to escape I'd have to reverse through it and probably then reverse out of the entrance. That'll be interesting if the cars are all still there when I need to head out tomorrow.