My drivers door won't set off any door open warnings, the interior light won't come on, the lights left on buzzer doesn't work, and when unlocked opening the drivers door doesn't get recognised so it relocks itself unless I open another door or start the car. I assume a sensor but I don't know where it is on these cars?

It's almost certainly a failure of the door open switch which is perhaps not surprising as the driver's door gets vastly more use. On the early Focus models the switch was mounted on the door frame next to the latch striker plate and protected by a corrugated rubber boot. This was superseded on later models by a switch integrated into the latch mechanism - another example of unnecessary and potentially expensive complication! I don't know at which model this change was made so hopefully one of the more knowledgeable members will be along to clarify.

Have the same issue with my mk1 cmax.

Have had the issue for a few months and not arsed fixing it as I'll have to replace the whole door mechanism.

It is annoying the whole locking itself thing.

Missus left the key in the Car once and the car locked itself .

Lucky we had a spare and could open the boot as the drivers door wouldn't open .