Three police officers are being investigated following an allegation they breached rules about honours nominations.

Temporary Chief Superintendent Parm Sandhu, the most senior Asian woman in the Metropolitan Police, is understood to have been served with a gross misconduct notice and placed on restricted duties.

Two other officers - a detective superintendent and an inspector, both from Frontline Policing - were given misconduct notices and remain on full duties, Scotland Yard said.

Temporary chief superintendent Parm Sandhu, right, has been placed on restricted duties after an investigation was launched into allegations of gross misconduct

Last month Ms Sandhu tweeted that she 'will be promoted to Chief Supt in Met' and said she will be the first woman of colour to hold the rank.

In 2006 she was presented with The Public Sector Award at the Asian Women of Achievement Awards in part for her work in the aftermath of the July 7 London bombings.

National Police Chiefs' Council guidelines state 'any person can nominate any other person for an honour' but people are not supposed to nominate themselves.

Some 27 current and former members of the police service were included in the Queen's Birthday Honours list last month.

A Scotland Yard spokesman said: 'The Met's Directorate of Professional Standards is investigating the conduct of three officers following an allegation that they breached guidelines relating to the UK honours nomination process.'