Take off the top cover, examine the interlock from behind and detach any rubber pipes or cables to try to open it from inside. If all else fails, the interlock itself may be faulty and will have to be broken open. A replacement interlock unit and/or catch will of course be required.
Check out www.2ndwave.co.uk/manual.html
Spares suppliers:
www.4directelectricals.co.uk
http://www.ukwhitegoods.co.uk
http://www.domesticspares.co.uk
http://shop.ezee-fix.co.uk
dannyboy
October 2008