BUCKINGHAM Palace banned "coloured immigrants or foreigners" from office roles until at least the late 1960s, according to new documents.

The papers, which were recently discovered at the National Archives, show the Queen's courtiers banned ethnic minorities from serving in clerical roles in the royal household.

The files also reveal how Buckingham Palace negotiated controversial clauses – that remain in place to this day – exempting the Queen and her household from laws that prevent race and sex discrimination.

The move is set to reignite the debate over the British royal family and race. It is part of the Guardian’s ongoing investigation into the royal family’s use of an arcane parliamentary procedure, known as Queen’s consent, to secretly influence the content of British laws.

The documents reveal how in 1968, the Queen’s chief financial manager informed civil servants that “it was not, in fact, the practice to appoint coloured immigrants or foreigners” to clerical roles in the royal household, but they were permitted to work as domestic servants.

It is unclear when the practice ended and Buckingham Palace refused to answer questions about the ban and when it was revoked. It said its records showed people from ethnic minority backgrounds being employed in the 1990s. It added that before that decade, it did not keep records on the racial backgrounds of employees.

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In the 1960s government ministers sought to introduce laws that would make it illegal to refuse to employ an individual on the grounds of their race or ethnicity.

But the Queen has been excluded from those equality laws for more than 40 years, which has made it impossible for people from ethnic minorities working for Buckingham Palace to complain to the courts if they believe they have been discriminated against.

In a statement, Buckingham Palace did not dispute that the Queen had been exempted from the laws, adding that it had a separate process for hearing complaints related to discrimination, but it did not detail what this process consists of.

The official documents reveal how government officials in the 1970s coordinated with the Queen's advisers on the wording of the laws.

In March the Duchess of Sussex, the family’s first mixed-race member, said she had had suicidal thoughts during her time in the royal family, and alleged that a member of the family had expressed concern about her child’s skin colour.

Some of the documents uncovered by the Guardian relate to the use of Queen’s consent, an obscure parliamentary mechanism through which the monarch grants parliament permission to debate laws that affect her and her private interests.

In 1968, the then home secretary, James Callaghan, and civil servants at the Home Office appear to have believed that they should not request Queen’s consent for parliament to debate the race relations bill until her advisers were satisfied it could not be enforced against her in the courts.

At the time, Callaghan wanted to expand the UK’s racial discrimination laws, which only prohibited discrimination in public places, so that they also prevented racism in employment or services such as housing.

A key proposal of the bill was the Race Relations Board, which would act as an ombudsman for discrimination complaints and could bring court proceedings against individuals or companies that maintained racist practices.

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In February 1968, a Home Office civil servant, TG Weiler, summarised the progress of discussions with Lord Tryon, the keeper of the privy purse, who was responsible for managing the Queen’s private finances, and other courtiers.

Tryon, he wrote, had informed them Buckingham Palace was prepared to comply with the proposed law, but only if it enjoyed similar exemptions to those provided to the diplomatic service, which could reject job applicants who had been resident in the UK for less than five years.

According to Weiler, Tryon considered staff in the Queen’s household to fall into one of three types of roles: “(a) senior posts, which were not filled by advertising or by any overt system of appointment and which would presumably be accepted as outside the scope of the bill; (b) clerical and other office posts, to which it was not, in fact, the practice to appoint coloured immigrants or foreigners; and (c) ordinary domestic posts for which coloured applicants were freely considered, but which would in any event be covered by the proposed general exemption for domestic employment.”

“They were particularly concerned,” Weiler wrote, “that if the proposed legislation applied to the Queen’s household it would for the first time make it legally possible to criticise the household. Many people do so already, but this has to be accepted and is on a different footing from a statutory provision.”

A Home Office official noted that the courtiers “agreed that the way was now open for the secretary of state to seek the Queen’s consent to place her interest at the disposal of parliament for the purpose of the bill".

The exemption was extended to the present day when in 2010 the Equality Act replaced the 1976 Race Relations Act, the 1975 Sex Discrimination Act and the 1970 Equal Pay Act. For many years, critics have regularly pointed out that the royal household employed few black, Asian or minority-ethnic people.

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In 1990 the journalist Andrew Morton reported in the Sunday Times that “a black face has never graced the executive echelons of royal service – the household and officials” and “even among clerical and domestic staff, there is only a handful of recruits from ethnic minorities”.

A Buckingham Palace spokesperson said: “The royal household and the sovereign comply with the provisions of the Equality Act, in principle and in practice. This is reflected in the diversity, inclusion and dignity at work policies, procedures and practices within the royal household.

“Any complaints that might be raised under the act follow a formal process that provides a means of hearing and remedying any complaint.” 

People who cannot immediately be removed would be stripped of benefits – placing them in the No Recourse to Public Funds (NRPF) category – and have their family reunion rights limited.

In the Queen’s Speech last month, she said that under the New Plan for Immigration legislation, measures would be “brought forward to establish a fairer immigration system that strengthens the United Kingdom’s borders and deters criminals who facilitate dangerous and illegal journeys”.

The plans have been branded “cruel and unfair”, with campaigners arguing that they “slam the door in the face” of people who could be in urgent need of the UK’s protection.

Enver Solomon, chief executive of the Refugee Council, said the plans “undermined” the UK’s “vital commitment” to providing protection to those in need by “unjustly differentiating” between refugees based on how they arrive.

“This is a cruel and unfair approach that slams the door in the face of people who could be in urgent need of our protection,” he added.