Vauxhall/Opel Astra H How to remove front door electrical connector

Pry up on top the center portion of the plug with a small screw driver and it will slide up and release the latch on the connector. Then the plug slides off.

Ben is correct, although I'd already figured it out by this point. This connector contains a weatherproof seal, which combined with the 34 pins would make it difficult to remove. So this plug cleverly has a clip whose main purpose is to evenly prise the plug out of it's socket as you slide it upwards. A very clever design.

Here it is released

And the red-herring is the clip which keeps the rubber boot in place. Shown here unclipped

Finally, I doubt there is anyone quite as stupid as me... but when you have to leave the car to go and get your multimeter - don't slam the door shut with the connector dangling loose. It won't end well!