You will be required to comply with this standard if you operate a B-double.
The prime mover of a B-double combination must be fitted with a front underrun protective device that complies with regulation 93 made under the United Nations Economic Commission for Europe (UNECE) agreement. If the prime mover has a date of manufacture after 31 December 2005, it must be fitted with a cab that complies with regulation 25 made under the UNECE agreement.
You will also be required to comply with this standard if you intend to exceed the maximum permitted gross mass on an axle group of a vehicle. If you comply with certain requirements set out in 12 BAA of the Interstate Road Transport Regulations, the maximum permitted mass limit on a single steer axle of a vehicle is 6.5 tonnes. One of these requirements is that the vehicle must be fitted with a front underrun protective device (complying with regulation 93 of the UNECE agreement) and a cab (complying with regulation 25 of the UNECE agreement).