A senior Metropolitan Police commander will be asked to account for the false information he gave MPs when he denied that plain-clothes officers were among the 2009 G20 demonstrations in London.
Giving evidence to the House of Commons Home Affairs Committee a month after the protest, in which thousands of demonstrators clashed with police, Commander Bob Broadhurst insisted there were no plain-clothes officers among the crowd, saying it would have been too dangerous.
But committee chairman Keith Vaz wrote to the Met's Commissioner Sir Paul Stephenson last week after questions arose about Mr Broadhurst's evidence in the wake of the unmasking of undercover policeman Mark Kennedy.
Mr Kennedy attended many demonstrations during seven years living as a spy among green activists.
The Metropolitan Police was forced to admit that false information had been given, issuing a statement correcting the testimony given by Mr Broadhurst on May 19 2009.
Mr Broadhurst told MPs then: "We had no plain-clothes officers deployed within the crowd. It would have been dangerous for them to put plain-clothes officers in a crowd like that.
"The only officers we deploy for intelligence purposes at public order are forward intelligence team officers who are wearing full police uniforms with a yellow jacket with blue shoulders. There were no plain clothes officers deployed at all."
But the statement conceded: "Having made thorough checks on the back of recent media reporting we have now established that covert officers were deployed during the G20 protests. Therefore the information that was given by Commander Bob Broadhurst to the Home Affairs Select Committee saying that 'We had no plain-clothes officers deployed within the crowd' was not accurate...
"The officers were covertly deployed by the MPS (Metropolitan Police Service) to G20 protests to identify individuals who may be involved in the organisation of criminal activity and to give live time intelligence/evidence as to the protesters' activity."
Mr Broadhurst has now been summoned to appear before the committee again to explain the inaccuracy of his earlier evidence. However, the Met stood by Sir Paul's assurance to the committee at the same hearing that the force did not use "agents provocateurs" - undercover officers actively fomenting unrest - at the protests around the world leaders' summit in April 2009.