Several major operators, including Jet2holidays and easyJet Holidays, have moved to stop selling these parks in recent months following pressure from wildlife groups, but Tui continues to sell them, although it has stressed this is under review.

The RSPCA has now joined other wildlife organisations such as Peta, World Animal Protection, Born Free Foundation, World Cetacean Alliance, Humane Society International/UK and Whale and Dolphin Conservation in writing to Tui’s managing director Andrew Flintham calling for the operator to change its stance on such attractions.

In the letter, the groups say: “There is ample scientific evidence showing that captivity is wholly incompatible with the complex needs of orcas and other dolphins."

They add that it would be “unconscionable” for Tui to continue selling tickets to marine parks now most of their major competitors have ended the practice.

Tui has previously said it is reviewing and reassessing its position on this issue – a move which has been welcomed by the wildlife groups.

But they add: “The organisation has been issuing this statement for many months. When can we expect the audit to be completed and for TUI to take decisive action on this matter?”

Musician and animal rights activist Morrissey, who supported Peta’s campaign to encourage Jet2 to change its policy on the issue, has also this week written to Flintham to urge Tui to follow suit.

In his letter, the former Smiths frontman said that Tui now had the “dubious distinction of being the last major travel provider in the UK” to continue selling tickets to marine parks with cetacean shows.

TTG has approached Tui for comment on the latest letters sent to the company about this issue.