A group of passengers who joined the Titanic Memorial Cruise in April is demanding refunds on a surcharge levied a month before departure, which cruise organiser Miles Morgan concedes was “a lot of money”.

Almost 950 of the 1,250 passengers received notice of a fuel surcharge of £15.50 per person per night, which equated to £325 for those booked for 21 nights.

Now a group of up to 200 is demanding a 50% refund. Spokesman David Cotton said: “What we object to is the magnitude and timing of the surcharge, the way it was calculated and the way it was allocated, with some passengers not having to pay. We feel the timing was insensitive.”

Cotton added: “Passengers have no criticism of the cruise.”

The group has challenged the basis on which Fred Olsen Cruise Lines – whose ship Balmoral was chartered by Morgan – calculated the surcharge and is threatening legal action after consulting Abta and Trading Standards.

Miles Morgan Travel has acknowledged an error in the surcharge and pledged to refund £1.62 per person per night.

Cotton told Travel Weekly: “We don’t think that is good enough.” He and his partner paid £4,500 each with the surcharge adding 7%.

Morgan said the cruise was priced four years ago when oil was $60 a barrel. He had allowed for a 50% increase, but the price had risen by more.

He said: “The case is a one-off. No one ever prices that far out. I feel sorry for the customers. But our terms and conditions are clear on fuel.

“We had to absorb the first 2% [increase]. Fred Olsen absorbed 5% of the fuel increase costs.”

He added: “I don’t feel we’ve been in any way negligent.”

Abta said: “We’ve investigated and Miles Morgan has complied with its legal responsibilities.”