A Belfast-born detective is suing Scotland Yard for more than £200,000, claiming he was subjected to sectarian bullying and harassment by his Protestant boss from Northern Ireland.
Detective Inspector Paul Armstrong, a Catholic, alleges that his former boss at the Metropolitan Police - Detective Chief Inspector Mark Roycroft (54) - discriminated against him because of his religious background, according to a report in the Daily Mail.
Mr Armstrong (49) - who is on long-term leave from the Met - claims he was subjected to bullying and harassment by Mr Roycroft.
Mr Roycroft, who is originally from Bangor, Co Down, retired from the Metropolitan Police in 2012 after a distinguished 30-year career, according to the newspaper.
Mr Armstrong alleges he was treated unfairly by Mr Roycroft in an annual appraisal, and that the criticism was motivated by "sectarian bias".
He is bringing a claim against the Met for religious belief, race and disability discrimination.
In his claim at Central London Employment Tribunal, Mr Armstrong said: "I was subjected to bullying and harassment by my then line manager DCI Mark Roycroft (an Ulster Protestant), who prejudiced me unfairly in my annual appraisal.
"He made comments that were untrue and misleading, which I sincerely believe were motivated by his sectarian bias towards Irish Catholics.
"This is direct discrimination.
"DCI Roycroft handed over my line management to DCI Gary McDade in July 2007.
"During this handover, he raised concerns to DCI McDade about my integrity and alleged that I was drinking alcohol whilst on duty, was not keeping the hours I was rostered to work, that I was keeping 'inappropriate associations'.
"He further stated his intention to formally place me under covert surveillance, which I believe he actually did. All of these allegations were without foundation, and again motivated by his sectarian bias."
Mr Armstrong told the employment tribunal: "It is my honestly held belief that DCI Roycroft's actions have directly and indirectly prevented any opportunities for my career development and progression."
The Daily Mail also reported that former colleagues of Mr Roycroft, who is now a college lecturer, described him as an officer of high integrity and said there was no substance to Mr Armstrong's claims.
His former colleagues said Mr Roycroft was a highly respected detective who had led a number of successful investigations in the Met and had also won a prestigious scholarship to carry out research into major criminal inquiries in the US.
The employment tribunal hearing - expected to last for 15 days - has been adjourned until later this month.