In 2003 I fitted a simple, but effective lock to my MGA boot. The basic idea was explained to me by my MGA specialist supplier - Bob West. I just altered the detail very slightly.

All that is required is an MGB-style glove box lock and a small U-clamp. I did not even have to go to Moss for the lock; my local ironmonger keeps them in stock.

The only destructive work required on the car is the drilling of a suitable diameter hole above the boot latch pull to accept the lock (see photo).