One of Britain's biggest holiday park operators has agreed to corporate changes after it was found to have run a secret blacklist targeting members of the Irish Traveller community, the UK equality commissioner has said.

Pontin's, which operates five camps in England and one in Wales, was investigated after a company whistleblower disclosed the list to the Equality and Human Rights Commission in February last year.

The EHRC said it had signed a "legally binding agreement" with Britannia Jinky Jersey Ltd, the parent firm of Pontins, forcing the company to change its booking system and hire new diversity officers.

British Prime Minister Boris Johnson's spokesman condemned Pontins' actions as "completely unacceptable". 

"No one in the UK should be discriminated against because of their race or ethnicity," he told reporters.

A list of "undesirable guests" circulated internally at Pontin's collated last names common in the Irish Traveller community, telling its booking agents that "we do not want these guests on our parks".

Many of the last names are common more widely in Britain and Ireland.

The list would have also barred some high-profile figures from politics, sport and entertainment, including people named Carney, Cash, Gallagher, Murphy and Stokes.

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Alastair Pringle, executive director at the EHRC, said the list recalled notorious signs in Britain from the 1950s when some landlords advertised rooms with the condition "No Blacks, No Irish".

"To say that such policies are outdated is an understatement," Mr Pringle said in a statement.

"It is right to challenge such practices and any business that believes this is acceptable should think again before they find themselves facing legal action."

Also speaking to RTÉ's News at One, Mr Pringle said Pontin's need to take a "pretty fundamental look" at how these policies and practices arose.

He said the EHRC has engaged Pontin's in a formal agreement and the company is going to conduct an investigation of the list to identify where it came, and to ensure appropriate action is taken.

The EHRC will monitor the observance of the formal agreement over the next 12 months, he said.

If the Pontin's operator fails to apply the required changes, it faces the prospect of a fuller investigation and eventual prosecution under Britain's Equality Act.

A spokesperson for the company said: "Britannia Jinky Jersey Limited has agreed to work together with the Equality and Human Rights Commission to further enhance its staff training and procedures in order to further promote equality throughout its business."

Some 58,000 people in England and Wales identified as Gypsy or Irish Traveller in the last census in 2011, with a further 4,000 in Scotland.

But the British government says there are likely to be 100,000 to 300,000 Gypsy/Traveller people and up to 200,000 Roma people living in the UK.