The Road Vehicles (Construction and Use) Regulations 1986

[F18.  This Part of this Schedule applies to a vehicle if with free acceleration, the coefficient of absorption of the exhaust emissions from the engine of the vehicle immediately after leaving the exhaust system exceeds—E+W+S

(a)if the engine of the vehicle is turbo-charged, 3.0 per metre, or

(b)in any other case, 2.5 per metre.]