A mortice lock fits into a slot cut out of the door, with a key hole on either face of the door, and it's 'striking plate' fits into a slot cut out of the frame. A mortice lock is deadlocking (i.e. can only be opened with a key). Strong locks are essential, choose one which conforms to British Standards. A five lever mortice lock should always be used on front or back doors. In fact, most home and contents insurers recommend a five lever mortice lock as a minimum. It is the most secure type of lock - to get past it without a key means the door frame itself has to be broken. The more levers that a key has to work, the harder it is for anyone to pick the lock. They are not difficult to fit providing you have the right tools.

1 Choose the position of the lock carefully. The normal position of the lock handle should be at a height of approximately 1 metre above the floor.

Do not cut into the door where the cross member joins the style as it will weaken the door

Hold the lock firmly in position, and mark the top and bottom of the lock case on the door. Then, using a marking gauge set to half the thickness of the door, join the marks to show where the centre line of the mortice lock will be.

2 Mark the exact depth of the lock case on the auger bit with a piece of tape.

3 Keeping the drill horizontal and square on the door, drill an overlapping line of holes down the centre line to the depth of the lock case.

If you're using power tools, don't forget:
o unplug them after use
o wear protective eye goggles *

4 Square up the top and bottom of the slot using a mallet and narrow chisel. Then smooth the sides of the slots with the wider chisel until the lock fits snugly into the door.