Sir Ian Blair described claims that he tried to block the promotion of a senior ethnic minority officer as "inconceivable" today.
The Metropolitan Police Commissioner was forced to defend his record on diversity robustly while giving evidence at an employment tribunal in Stratford, east London.
Commander Shabir Hussain, one of his most senior colleagues, has claimed that he was repeatedly overlooked for promotion in favour of white candidates.
The 45-year-old officer has alleged racial discrimination against the Metropolitan Police Authority, its chairman Len Duvall and Sir Ian.
Mr Hussain said his application to become deputy assistant commissioner was rejected an unprecedented four times despite being better than other hopefuls.
But Sir Ian strongly denied the claims today.
He told the hearing: "It is inconceivable that I would seek to block the promotion of a senior ethnic minority officer and any suggestion to that effect would be seen as an extraordinary aberration. I refute it totally."
Mr Hussain claims he was treated "less favourably" in terms of race on several occasions and was appointed to less sought-after roles within the force rather than promoted to a higher position.
He has accused Sir Ian of having a "golden circle" of "favourite sons and daughters" earmarked for promotion to the top of New Scotland Yard.
Rabinder Singh QC, for the Met, asked Sir Ian if he had indeed operated a golden circle.
He replied: "I entirely refute that allegation. The Metropolitan Police service has a proud record of meritocracy."
Sir Ian, speaking always in calm hushed tones, explained to the hearing the make-up of his senior team, which consisted of eight deputy assistant commissioners and 25 commanders.
He said he was assisted by a team of one deputy commissioner, four assistant commissioners and four directors.
Mr Hussain was transferred to the traffic/transport command in 2005 and claims he was not offered the chance to serve as a crime commander, which he said placed him at a disadvantage for gaining promotion.
But Sir Ian told the hearing that the traffic and transport role offered Mr Hussain "a very real opportunity to demonstrate that he would be able to perform at DAC rank".
He added: "I therefore do not agree that he was placed at a disadvantage in being transferred to the traffic and transport command."
Mr Hussain has also claimed that Sir Ian treated him "less favourably" in the 2006 DAC promotion process and that he lobbied for the eventually successful candidates.
But Sir Ian argued that this was not the case and explained that Mr Hussain's interview performance had not been particularly good.
He said: "I'm informed that Commander Hussain alleges that I treated him less favourably in the 2006 promotion process in that I supported and/or lobbied for the successful candidates. This is simply incorrect and baseless."
He said each candidate had been assessed on the grounds of the chief officer's separate assessment and their performances during the interview process.
Under cross-examination from Mr Hussain's lawyer, Martyn Barklem, Sir Ian explained that it was extremely difficult to rise to the rank of commander.
He told the hearing that hundreds of candidates would apply for the rank held by Mr Hussain but only a tiny proportion would be successful.
He said: "A commander is already a very, very senior rank - beyond that the numbers get smaller and smaller."
He added: "I don't think that someone reaching commander has in some way failed."
Mr Hussain had shown a good track record of achievement and work and the fact that he had not yet been selected as DAC was down to the nature of competition, Sir Ian said.
And he added: "I have championed issues of diversity throughout my career as a senior police officer."
Listing his efforts in attempting to achieve diversity within the force he noted a speech he made in 1999 about inclusivity in policing.
He said the speech "was widely seen as the police service's acceptance of the forthcoming Macpherson Report into the racist murder of Stephen Lawrence".
Sir Ian said that once appointed Deputy Commissioner he had created a diversity directorate which drove the acceptance of diversity through the Metropolitan Police.
He said he was often invited to speak at conferences held by the Black Police Association, the Association of Muslim Police and other independent advisory groups.
He also disclosed that he was a mentor to a senior black public figure.
He added: "In speech after speech I have made clear the operational necessity of diversity in policing and have referred repeatedly to my belief that we have to make the Met look like London."
Mr Hussain is the second senior officer to level claims of racism at the Metropolitan Police in recent weeks.
Mediation is taking place behind the scenes to defuse a row between Assistant Commissioner Tarique Ghaffur and Sir Ian.
It emerged last month that Mr Ghaffur had compiled a dossier of evidence supporting claims he was undermined and humiliated.
Backed by the National Black Police Association, Mr Ghaffur said he was sidelined in his role preparing the security operation for the 2012 Olympics.
But Sir Ian publicly warned Mr Ghaffur to step into line, saying every member of the force "works to my direction and must meet my reasonable requirements".Reuse content