That's what's being alleged by Liberal Democrat MP Tom Brake to the House of Commons joint committee on human rights. The committee sat yesterday for an evidence session on policing and protest and Brake reiterated what the New York Times was reporting in the days after the protests: that undercover police had been in the crowds, trying to incite violence.
Brake was at Bank on 1 April acting as a legal observer. He told the Guardian:
"When I was in the middle of the crowd, two people came over to me and said, 'There are people over there who we believe are policemen and who have been encouraging the crowd to throw things at the police'". But when the crowd became suspicious of the men and accused them of being police officers, the pair approached the police line and passed through after showing some form of identification.
The Met have flatly denied the accusations, and the IPCC say that of the 256 complaints they've received about G20 policing, none relate to agents provocateurs.