90% of locks fitted to upvc doors are the same as yours so its not unusual to have one on your front door,you can buy a lock that engages to the locked possition when handle is lifted or one that has a snib to lock it on inside,you might get one from www.northwesthardware.co.uk to match the one you alreay have and do it yourself if you are confident enough,or get a double glazing repair engineer or locksmith to do it for you but it will cost a lot of money,why dont you fit a euro cylinder with a thumb turn so you can close your door then turn the thumb turn and door is locked it will be much cheaper and you will get the same result.hope this helps
shaun www.sdwupvcrepair.co.uk, June 2008