Deadlocks operate in a simple way! They have a bolt that is thrown out of the mechanism each time you lock the door. This bolt must slide smoothly into a small hole found at the opposite side of the door and onto the doorjamb. There's an iron plate, which is called strike plate. If the bolt does not meet the hole, the door won't lock. This would cause tremendous security problems since the door could be kicked down or opened easily. The main reasons for deadbolt problems are related to alignment issues. When the door is shut, the bolt must be in perfect alignment with the strike plate. In a different case, it would mean that the door binds, the lock mechanism is damaged or the strike plate is loose. Such problems are often fixed with a few moves unless worse issues are hidden behind the obvious ones. In the case of the latter, you might want to replace your British standard locks.
Let's consider easy fixes related to the door itselffirst. Don't forget that the security locks are installed on the door. If the door sags, it won't close well and won't lock. If the door closes but sags, the bolt won't be aligned with the strike plate. You must make sure the hinges of the door are tightened but not too much or you'll have similar problems.
If the problem is caused by the loose strike plate, your intention is to tighten it. If you find that the screws are too small to hold the plate, replace them with larger ones. Under normal conditions, you'll see the marks left on the doorjamb by the strike plate's original position. So, you'll know where to place the strike before tightening it. If there are no marks, follow a different process. With the door open, lock so that the bolt will be thrown out and let it rest against the jamb. Mark with a pencil the position of the bolt (above and below the bolt) and see how far you must push the strike plate before tightening it.
If the problem comes from the lock mechanism, door lock repair would include lubrication. Try spraying lubricants in the keyhole and if that doesn't work, dismantle the lock in order to clean and oil it correctly. In this case, you will have to remove the rosette and possibly the handles before unscrewing the bolts keeping the lock in place in order to remove the mechanism for maintenance. If the mechanism is damaged, lock replacement is in order.
Locksmith Beckenham, 020 3608 0419, Worsley Bridge Rd, Beckenham, United Kingdom, BR3 1RW, http://www.locksmith-beckenham.co.uk/