This paragraph applies if an English and Welsh constable or an enforcement officer has reasonable grounds to suspect that an offence under section 1 or 2 has been, or is being, committed on the ship.

The constable or enforcement officer may arrest without warrant anyone whom the constable or officer has reasonable grounds for suspecting to be guilty of the offence.

The constable or enforcement officer may seize and detain anything found on the ship which appears to the constable or officer to be evidence of the offence (but not including anything that the constable or officer has reasonable grounds to believe to be an item subject to legal privilege).