how do I get a barrel out of double glazed door that is locked and lost key?

If the existing barrel is not an anti-snap sdesign, you may be ableto snap it (you may trash the handle escutcheon as well)

https://www.youtube.com/watch?v=TCufUpr_QRY

http://www.locksmiths.co.uk/about/public/cylinder-snapping/

http://www.londonlocksmith.co.uk/page/id/129

http://www.instructables.com/id/How-to-pick-a-common-cylinder-lock/

https://www.youtube.com/watch?v=D2Z0ZN9hvOw

https://www.youtube.com/watch?v=rHZZCEP5lPI

http://tradelocks.co.uk/domestic-locksmith-tools/signature-range-tools/nigel-tolley-plug-puller.html

Make sure your new cylinder is the right length inside and outside.

Or call a locksmith
August 2015