Police Commander Bob Broadhurst apologised today for misleading MPs about the use over undercover officers at the G20 protests.
Mr Broadhurst admitted to the home affairs select committee that he had given "inaccurate" evidence that there had been no undercover police at the G20 protests in April 2009.
He said to MPs: "May I first of all apologise" for giving them "information that now appears to be inaccurate."
Mr Broadhurst had insisted in May 2009 that the Metropolitan Police "had no plain-clothes officers in the crowd" at the G20 protests.
But the Met were forced to admit he was wrong following a series of revelations sparked by former police spy Mark Kennedy's admission he was involved in the G20 protests.
Mr Broadhurst admitted he should have known about the deployment of undercover officers and said there was a review going on as to whether he should have asked or should have been informed.
Val Swain of Fitwatch, which monitors the police teams who gather intelligence on protesters, called for "a much greater level of honesty from the Met" over its policing of activists.
Scotland Yard chief Sir Paul Stephenson claimed after the G20 protests that using agents provocateurs would be "wholly antithetical to everything I have known about policing for the best part of 34 years."
Ms Swain said activists now needed to know "how undercover and plain-clothes police have been used on protests in the recent past."
She warned that undercover officers "have the ability to manipulate the behaviour of crowds - there cannot be any justification for this.
"We must make clear that there cannot be any justification for putting undercover police officers in protests, interfering with people's basic rights."
London Mayor Boris Johnson came under fire from Labour London Assembly Member Len Duvall for his "deafening silence" over the string of scandals facing the Met.
In his election manifesto, Mr Johnson pledged to take "personal responsibility" for the force.