Effective from 1st October 2015, Building Regulations Approved Document Q sets security requirements for new dwellings in England.  (There is a corresponding Approved Document Q for Wales.)

Reasonable standards for doors and windows are required to resist physical attack by a casual or opportunist burglar.  To meet the requirements, reasonable provision must be made to resist unauthorised access to any dwelling and any part of a building from which access can be gained to a flat within a building.

The requirement can be met by windows and doors that achieve PAS 24 and with laminated glass with minimum of class P1A in accordance with BS EN 356 (glass in building - resistance to manual attack).

6.8 mm Pilkington Optilam™ achieves Class P1A (in fact, as high as P2A), but 6.4 mm does not achieve Class P1A.