CRESSIDA Dick's first official engagement on the afternoon she became the Commissioner for the Metropolitan Police was to attend the funeral of PC Keith Palmer, the officer killed in the March Westminster terror attack.

Saturday's murders in London is the first major terrorist incident she has had to deal with, less than two months into the biggest job in UK policing.

But before her appointment the family of the innocent man shot dead in an operation she commanded in the fall-out from the 2005 London terror attacks said she should not be considered for the role.

The family of Jean Charles de Menezes said Ms Dick’s part in the disaster meant she could not “command public confidence” as commissioner of the Met.

In the immediate aftermath of 21 July 2005 London bombings, Ms Dick was the gold commander in the control room during the operation which led to the death of Mr de Menezes, wrongly identified as a potential suicide bomber.

The 27-year-old Brazilian national was repeatedly shot in the head at Stockwell tube station in south London.

Officers believed he was would-be suicide bomber Hussain Osman who lived in the same block of flats as the Brazilian. When the force was later found guilty of breaching health and safety laws, the jury cleared Ms Dick of blame.

She spent three days giving evidence and told the jury she was told five times that surveillance officers thought a man they were following was Osman.

Ms Dick said in 2007: “From the behaviours described to me, nervousness, agitation, sending text messages, using the telephone, getting on and off the bus, it all added to the picture of someone potentially intent on causing an explosion.”

At a 2008 inquest, she said: “If you ask me whether I think anybody did anything wrong or unreasonable on the operation, I don’t think they did.”

The inquest jury returned an open verdict, seen as demonstrating its members were unconvinced by the police account of events.

When she was named the successor to Sir Bernard Hogan-Howe in February the family of Mr de Menezes released a statement condemning the move.

They said: "We had to face a tragedy that no family should ever have to experience; the tragic death of a loved one at the hands of those we entrusted to serve us and protect us.

"At the helm of the police on that fateful day when Jean was killed was Cressida Dick. The message of today's appointment is that police officers can act with impunity.

"The commissioner of the Metropolitan police is the most senior police officer in the country, a post that is expected to uphold the highest standards of professionalism, to command public confidence and be responsible for ensuring that the police act lawfully and are held to account."