What did you do with whatever else you've got?

[Gnasher]

Yep it's the twist type. Look at 12 O'Clock and you'll see the locking tang there's the same at 6 O'Clock.  Grip the down each side of the black plug where you can see it's locked into the metal tang (each side) twist anti clock wise, you only need approx 1/8 of a turn, just enough to get the locking tang out from behind the prong. 

They can be stuff as mentioned.