Armoured tracked vehicles had been driving at up to 20mph since 1977 . But it emerged in 2013 they were not exempt from tracked vehicle laws . Limit was then halved to 40mph , but DfT now wants to raise it to 20mph . Ministers believe 40mph limit is causing congestion and health concerns .
Armoured tracked vehicles had been driving at up to 40mph since 1977 . But it emerged in 2013 they were not exempt from tracked vehicle laws . Limit was then halved to 20mph , but DfT now wants to raise it to 40mph . Ministers believe 20mph limit is causing congestion and health concerns .