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From 2007 NHBC Standards:

SECURITY
Items to be taken into account include:
(a) locks to main entrance doors
DWELLINGS
The main entrance doors of individual
dwellings should be fitted with one (or
more) securely fixed lock and keep which
complies with BS 3621 or has:
• at least 1000 differs, and
• a fixing which, if burst open, would not
pull out without breaking the door or its
frame, and
• a hardened steel bolt or inserts to
prevent sawing, and
• latch and deadlocking facility
and is preferably openable on the inside
by a single simple manual operation not
requiring the use of a key.
Any glazing which, if open or broken,
would permit release of the snib by hand
or arm entry should be laminated.
Multipoint locking systems (espagnolettes)
are alternatives to conventional locks
provided they meet with the above
requirements.
FLATS AND MAISONETTES
Locks to entrance doors of individual flats
and maisonettes of three or more storeys
should be openable from the inside by
a single simple manual operation not
requiring the use of a key.
To avoid the possibility of the door
becoming locked during a fire while one of
the occupants is outside the dwelling the
lock should not have a self locking latch.
(b) opening limitation devices to main
entrance doors
A securely fixed opening limitation device
should be fitted to main entrance doors.
Opening limitation devices should be fitted
to the entrance doors of individual flats
and maisonettes.
In sheltered accommodation opening
limitation devices should be of a type
capable of being disengaged from the
outside with a key.
(c) view outside main entrance door
There should be a means of giving a wide
angle view of the area immediately outside
the main entrance door of individual
dwellings. Acceptable ways include:
• a through-door viewer
• clear glazing either to part of the door
or a convenient window
• closed circuit television.