OIC.

Hmm, reckon it might just be a case of undoing the screw at the bottom
then and wiggling about to see what happens. From that pic it does
look like it might clip in place at the top.

I managed to sort it in the end.
Behind the lever there is a panel which pulls out, to reveal a screw. Its a
complete bitch to get out and isn't that obvious it does come out.
All I need now its to get some tweeters! I just wanted to check I can fit
some myself before buying some.

Andy M