Just saw your title. So: Its a window. Probably UPVC.
http://howtomendit.com/answers.php?id=172761
http://www.diydoctor.org.uk/forums/how-to-fit-a-new-handle-to-a-double-glazed-window-t12099.html
http://www.oople.com/forums/showthread.php?t=36700
http://upvcspares4repairs.co.uk/faq
You may get some mileage asking in the above forums, January 2017