Then-Northern Ireland Secretary Peter Brooke said in a letter to Government colleagues that implementing the Act was “crucial to the success of all our NI policies”, according to the declassified files.

The Fair Employment Act 1989 was enforced until superseded by the Fair Employment and Treatment (Northern Ireland) Order 1998, which came into operation on 1 March 1999.

The 1998 Order is still in place today, as amended in 2003 to implement the EU Framework Employment Directive.

In a 1989 letter written by Mr Brooke to Tom King, a former Northern Ireland Secretary who then served as Defence Minister, Mr Brooke included a reminder of employers’ responsibilities under the Act.

Those included monitoring of the religious composition of the workforce and regulation of recruitment, raining and promotion practices.

Mr Brooke added: “As you know, the successful implementation of this tough and radical piece of legislation may be crucial to the success of all our NI policies in relation to perceptions abroad, especially in the United States.”

He continued: “We have rightly given a very high political priority to this legislation.

“As Douglas Hurd and you have said, it is unacceptable in a civilised society that Catholic males should be more than twice as likely to be unemployed as Protestants in NI and it is understandable that that should be a source of grievance to the minority community.

“Even if we are not able in the event to improve the statistics very quickly, we can demonstrate our commitment to equality of opportunity for all by determined implementation of the new Act.”