Go to: http://www.espares.co.uk/parts/washing-machines/door-parts/indesit/p/1556/805
Sounds like you need a new door interlock. Look for part no: ES548529 but do a final compatibility check yourself.
Whilst there click on the Advice Centre tab. and look for the video which shows you how to do it. Try looking at the bottom of Washing Machines-page 3 (forget the AEG make bit-there all the same)
GB in Wales, March 2013