Hi I am a window & door repair man and have come across this problem many times.
1. Remove the internal and external handles by undoing the internal screws. (mostly two screws but sometimes three)
2.Take a pair of mole grips (medium duty/ size) and lock on to about 10 mm of the Euro cylinder (its the bit you put the key into)
3. The lock needs to be snapped so a swift sideways motion is required.
4. Once the lock is snapped you have access to the main lock and should be able to insert a screwdriver and flick back the lock to allow the handle to be depressed and the door opened.
You will need to fit a new Euro cylinder and this can be bought online .. see link
http://www.hdhardware.co.ukproduct_info.php?products_id=236
They come in different sizes and advice on which one to order can be had at www.hdhardware.co.uk
Hope this helps
The House Doctor, October 2009
