It's best to have the deadlock one-third up from the bottom of the door (kick height) and a nightlatch one-third down from the top (shoulder height). That way you have the strength spead, and not concentrated in a single point.
Many homeowners fall into the lazy trap of only ever using the nightlatch, except perhaps when they go on holiday. Unless everyone in your house is immune to that, you need a BS nightlatch; which is of similar size, but much stronger and heavier, and is also more expensive than a useless lower-priced traditional Yale. A nightlatch should be well away from the letterbox and any glass since it can easily be opened otherwise (but BS nightlatches have the facility to deadlock the internal knob, if you remember to use it).
If you ever watch a cop show on the TV and someone forces open a door with his shoulder, it will usually be a traditional yale-type lock that gives way.
Ideally you would have both a BS deadlock and a BS nightlatch. Some locksmiths recommend two deadlocks and a nightlatch; but my opinion is that most homeowners won't bother to lock them all.
If you can only afford one BS lock, have the mortice deadlock. It is cheaper and stronger than the nightlatch. The Union J-2134E was a Which Best Buy.
People with plastic doors will have to use some kind of multi-point locking, usually with a Eurocylinder. They are almost certain not to meet the British Standard, but hey, some people like plastic doors.
Locks with a notched cylinder key (like a Yale or most Eurocylinders) can be attacked in a couple of low-skill ways that 5-lever locks can't, but burglars usually won't bother. It is usually easier to get in through a window or back door, especially if poorly protected or left unlocked.