I've got a Focus Vignale estate that's got something that niggles me. If I didn't have a dashcam plugged into the 12V/cigarette lighter socket I probably wouldn't have noticed it. Anyway, it cycles randomly through powering off a) when the ignition is turned off b) when a door is opened or c) doesn't power off. But linked into this is locking the doors by touching door handles. In case b) locking works on all the doors but for a) and c) locking (and unlocking) only works on the driver's door

 

Any thoughts or suggestions would be much appreciated

Battery. 
 

If you have a low battery charge the car shuts off the 12v socket as soon as the engine goes off. It also shuts off power to all the keyless handles except the drivers door. 
 

If the battery is charged enough the 12v socket stays on until you either open the door or within something like 30mins of engine off.  
 

Sounds like you are hovering just over and under the cars low battery threshold. 

Thank you Alex. I bought the car at 10 months old with only 1600 miles and I've wondered about the battery as the stop/start rarely works.

And I thought low battery problems were the reserve of my Alfa,,,,,,

Mk4 Focus have battery issues that’s for sure...

From honest John .....

17-12-2019: Numerous electrical faults reported in new Ford Focus 1.5 Ecoboost 8-speed automatic since summer 2019: "Charging System Alert!! Service Now! warnings, displays changing randomly, the seatbelt warning alarms going on even when the engine was switched off, and so on. Fearing imminent breakdown owner called out the RAC. After connecting his diagnostic interrogator to the car it revealed dozens of different faults including low voltage to the brake servos and steering servos etc. etc. After a lot of head scratching he looked under the bonnet and found a faulty battery earth connection. The earth bolt was only partly inserted into the body, cross-threaded and the cable was making and breaking connection. (See 2-1-2019 and 23-1-2019 above.)

As simple as that?!?