Part III of the Transport Act 2000 authorises the Secretary of State to make, amend or revoke a trunk road charging scheme in respect of roads for which the Secretary of State is the traffic authority, and which are carried by a bridge, or pass through a tunnel, of at least 600 metres in length. The M4 and M48 Motorways (Severn Bridges Charging Scheme) Order 2017 (“the 2017 Order”) introduced a charging scheme in respect of the roads carried by the Severn Bridges (“the bridges”).