I can confirm that it is possible to remove the door panel when the door is locked shut. I can't explain how I did it as I just used sheer bloody minded determination, a lot of wiggling and twisting, and I motored the seat back and forth a lot it just sort of came of in my hand.

As a result I have released the stuck levers and can now get in and out again from the inside. It looks like the carrier may have broken again but I'ts gonna be quite a while before I have the time to take a proper look.

Cheers for all the advice

Mike