May 29 2003
From 30th September 2003, all new commercial and public buildings with a gross floor area of 1000 m2 or more must meet the new airtightness standard of 10 m3h-1m-2.
This is covered by Part L2 of the Building Regulations and as a result, new buildings have to be tested for air permeability. Until now a standard of 'reasonable compliance' has been acceptable but the stricter regulations will soon be enforced.
Additional information can be found at BRE
Source: BRE