Nothing in this Act shall authorise the levying of tolls in respect of—
(a)a vehicle identifiable by writing or markings on it or otherwise by its appearance as being the property of—
(i)a police authority;
(ii)a fire authority as defined in the [1947 c. 41.] Fire Services Act 1947; or
(iii)one of the civil defence forces or the civil defence services as respectively defined in the [1948 c. 5. (12, 13 & 14 Geo 6)] Civil Defence Act 1948;
being used in the execution of duty;
(b)an ambulance or other vehicle if it is being used by a health authority (as defined in the [1977 c. 49.] National Health Service Act 1977) or by a voluntary organisation or other person under an arrangement made under that Act;
(c)any other ambulance if it is being used for the purpose of or in connection with the transport of persons requiring or receiving medical treatment or for the carriage in an emergency of medical apparatus or supplies;
(d)a vehicle exempted from duty under section 4(1)(g) of the [1971 c. 10.] Vehicles (Excise) Act 1971 if it is being used for the purposes of an invalid; or
(e)a vehicle so exempted under section 7(2) of that Act if it is being used by or for the purposes of a person suffering from a physical defect or disability.