Rule 46
These vehicles MUST NOT be used on motorways (see Rule 253 ). They should not be used on unrestricted dual carriageways where the speed limit exceeds 50 mph (80 km/h) but if they are used on these dual carriageways, they MUST have a flashing amber beacon. A flashing amber beacon should be used on all other dual carriageways (see Rule 220 ). Laws RTRA sects 17(2) & (3) , & RVLR regs 17(1) & 26