ECU connections - how to disconnect

Specifically the green and grey connections behind the ECU. I cannot separate them.

I have tried to separate the from the steel surround but no luck, and I have tried to just separate them by pressing on the side closest in the photo (Which releases the clip and I have then tried to release with a screwdriver) and pushing outward on the side next to the surround. Must be something simple

When I released mine, it was to grip it hard on those parallel ridged section at the wire end in your picture and squeeze, pulling parts away from each other. From recollection, they were a firm fit.

I'll answer my own question in case someone has the problem.

To separate the plug from the backing plate you push the lug outwards and then you can pull the plug upwards and the out to separate. You can then separate the 2 halves of the plug. Wasn't obvious to me.

I have been known to use an electrical screwdriver down the side of the clip to release.