A concrete lobby group has hit out over a call by security service MI5 to replace the concrete blocks protecting the Houses of Parliament with steel barriers.

The move has come after MPs were warned that the concrete blocks could become lethal projectiles in the event of an attack by suicide bombers.

Alan Bromage, head of civil engineering at The Concrete Centre, said that concrete barriers are a proven security success for the protection of high-profile buildings throughout the world. He added that their strength, robustness and mass were unrivalled.

Bromage asked: “What about the effects of lethal steel shrapnel in an explosion at a steel barrier?”

MPs have also been warned about the vulnerability of the Big Ben clocktower, as it is near a busy road and has recently been climbed by Greenpeace protesters.