David Pickavance, chairman of the Air Tightness Testing and Measurement Association, who is also general manager of testing services at BSRIA, said most buildings of more than 1000 m2 did not conform to the regulations.
He said: "Two-thirds of newly built commercial building are not being tested."
Research group BRE and Chiltern Dynamics, a testing body, said half of commercial buildings tested failed to meet minimum standards.
BRE said commercial buildings were struggling to meet the present air-permeability standard. This states that a building should leak no more than 10 m3/h/m2 at a pressure of 50 Pa.
Richard Bate of Chiltern Dynamics said commercial buildings would find it harder to pass the 5 m3/h/m2 standard that was being considered for the next revision of Part L in 2005. Bate said: "Of the buildings we have tested in the past year, barely 10% would have been able to achieve it."
The government's current thinking is that permeability should be 7 m3/h/m2 for mechanically ventilated commercial buildings. The figure for residential dwellings could be set at 5 m3/h/m2.