Reg.15 of the Public Contracts Regulations 2015 (PCR2015) establishes coverage rules for defence and security procurement that aim to coordinate the general rules with those of the Defence and Security Public Contracts Regulations 2011 (derived from the transposition of Directive 2009/81).
The content of reg.15 is identical to that of Art 15 of Directive 2014/24 with some minor drafting and structural changes, which deserve no further comment (cf Pedro's more elaborate view here). For an in-depth analysis of the rules applicable to defence and security procurement, as well as the coordination issues that such a special regime creates, see M Trybus, Buying Defence and Security in Europe. The EU Defence and Security Procurement Directive in Context (Cambridge, CUP, 2014).