Cruise ships sailing in UK waters will be limited to 1,000 passengers when operations begin on or after May 17th.
All travellers must also be residents of the British Isles, according to new regulations issued by the department of transport.
The rules also state Covid-19-secure guidance will continue to apply.
Groups of more than six people or two households will not be allowed to mix indoors – whether or not they originally booked in the same group, the government said.
Only passengers who are resident in the UK and the Common Travel Area – comprising the Republic of Ireland, the Channel Islands and the Isle of Man – will be allowed to board a cruise from a British port.
Authorities hope to relax the regulations on June 21st, in line with a wider reopening of the UK economy.
At this time, the government hopes to remove all legal limits on social contact – which will include lifting capacity limits for domestic cruises.
The first cruise is expected to be aboard MSC Virtuosa, which is performing her inaugural season around the British Isles.
She will depart from Southampton on May 20th on a four-night voyage which will call halfway through at Portland in Dorset – 50 miles south-west.
Her passenger capacity is around 5,000, indicating occupancy of around 20 per cent if all 1,000 legally permitted places are sold.