Pull the door card off- its probably either a grub screw has fallen out of the handle inside the door, or the lever that actuates the lock inside the door has gone for a burton....
Thanks Simon, small plastic grommit had popped out of a alli plate...not very well engineered as can see most probably happen again. Cheers
Viper, thanks also though found locks on my trad Super Sport very different arrangement to the Aero (with Morgan can be different from one Aero to another to I guess

)