(Updated 10:50 a.m. BST) -- P&O Cruises has further extended the suspension of cruise operations until April 2021 in response to the "current uncertainty around European ports of call".
The line has already cancelled two world cruises scheduled for next year on Aurora and Arcadia.
P&O Cruises originally announced a 30-day suspension on March 16, following CLIA's recommendation for cruise lines to voluntarily and temporarily pause operations, before extending for a second time on March 30 through May 14, a fourth time through July 31, a fifth through October 15 and a sixth through January 2021.
P&O Cruises president Paul Ludlow said: "With hopeful news headlines clearly we do not want to extend our pause in operations any further than absolutely necessary, but given the ever changing guidance around international travel and the varying regulations in many European ports of call we felt it prudent to cancel these additional dates.
"In addition, as the final payments are due for these cruises very soon we felt it was the right thing to do for our guests.
"We are so sorry to disappoint those who were due to travel but really hope they will re-book for later in the year or for our new programme of 2022 holidays which went on sale earlier this month with strong demand, showing great confidence in cruising in the future."
Less than three weeks ago Ludlow said he was confident of a March restart date. He said at the time: "I don't think it's impossible," but said the line need to wait and see what happens in terms of the UK lockdown, which is due to ease on December 2.
It is not exactly certain which will be the first cruise to restart, but it looks as if most April cruises are cancelled and a May 2021 restart looks more likely. The furthest out cruise to be cancelled is a Europe fly/cruise on Azura on April 22, 2021.
Most of the P&O Cruises fleet is currently moored off the south coast of England and it's possible to see the ships on so-called "Ghost ship tours" from Mudeford.
At present, there is a blanket ban on all ocean cruising from the Foreign, Commonwealth and Development Office, despite calls from Cruise Lines International Association to lift the ban.
All passengers who were booked on these cancelled sailings will receive an enhanced Future Cruise Credit which gives an additional 25 percent on top of the amount paid for the holiday.
All passengers with bookings on a cancelled cruise will be notified and will automatically receive an enhanced 125 percent Future Cruise Credit or alternatively a 100 percent refund.