When a ship is navigating in a pilotage district, and has on board a pilot licensed for that district, or a master or mate holding a pilotage certificate for that district, the master of the ship shall cause a pilot flag to be exhibited; and if he fails, without reasonable cause, to do so, he shall be liable on summary conviction in respect of each offence to a fine not exceeding—
(a)in England and Wales and in Scotland, level 4 on the standard scale,
(b)in Northern Ireland, £500.