The car unlocks and locks fine and sounds ok when it does.
When the key is turned to position 1, all of the lights come on as you'd expect.
So, obviously the car battery is OK, however,
When you turn the key to position 2 to start the car, you may hear a clunk, sometimes the speedo lights go out for a split second before coming back on, a key symbol appears on the speedo LCD and the car does not start.
Because of the previous events, it may not be obvious, however, it's a cheap and easy fix.