We were asked to secure a commercial premises following a break in. The existing lock on the external door was a 3 lever, only really suitable for an internal door or bathroom, certainly not the main entrance.
Because of the badly fitted door the original lock bolt only entered the keep by about 2mm. The burglar simply pushed the door and the frame apart to get in.
A BS (British Standard) 2007 mortice lock has a minimum bolt throw of 20mm and makes it much more difficulty to prise door and frame apart. In addition there are specifications for minimum key differs, sawing and drill resistance.
