New Hotpoint door interlock faulty?

I have just replaced the door interlock on my Hotpoint Aquarius WM64 as the machine gave a pop/bang after being set on a wash programme recently. I replaced the fuse and it ran as normal but the door would not release when the programme had finished. I had to be quite forceful in 'disconnecting' the interlock by snapping it in half in the madchine and disconnecting the latch from the electrics. The replacement will not work however. The tiny catch/lock under the 'sliding catch' never comes out to prevent the sliding part from retracting even when it should be activated. When I put the older electric section of the broken lock back on, the door lock LED instantly illunuinated. Swap the new one back on and nothing. Is this new part definately faulty or should I look at something else?