there are way of opening the door like taking off the handles and drilling out a bit of the door from behind the handles to find the art of the mech that will allow you to do this , i would not advise on doing this one yourself as it could cost you more than paying a good locksmith if you get it wrong .
where in the uk are you?
do you know if the mech has hooks, rollers or dead bolts there are thousands of different ones on the market?
contact me if you are stuck
24hr.locksmiths@googlemail.com
dave, September 2008