The police watchdog is investigating allegations that an officer colluded with colleagues to arrest a young activist on "false grounds" at the student fees demonstrations.
The Independent Police Complaints Commission said it was investigating the "serious allegation" that an officer abused his position after a 20-year-old protester breached the cordon during the demonstrations in Parliament Square last December. Commissioner Rachel Cerfontyne said: "We will also be looking at the circumstances of how the man suffered a broken tooth during his detention."
Three officers have been told they are being investigated for alleged criminal and gross misconduct matters. The 20-year-old was injured as he was chased and caught by police.
One officer was wearing sound-recording equipment which captured the chase and detention as well as a subsequent conversation between a number of colleagues, the IPCC said.
"The investigation will look at an allegation that the officers conspired to falsely arrest the 20-year-old, as well as how he sustained the damage to his tooth," the IPCC said.
Meanwhile, the anti-cuts protest group UK Uncut has announced plans to target the flagship stores of some of Britain's biggest retailers and banks as part of a day of demonstrations taking place across the country on 26 March.
Activists will attempt to occupy the Oxford Street outlets of organisations including Vodafone, Boots, Tesco, Topshop and Dorothy Perkins as well as those of RBS, LloydsTSB, NatWest and Barclays, all of whom the group accuses of "tax-dodging".
The protesters said they intend to turn the branches into creches, libraries and homeless shelters – services being closed due to government cuts. They added that a second protest would take place later in the afternoon, but refused to say where.
Organisers refused to call on protesters to refrain from violence during the demonstrations, which coincide with the nationwide protests organised by the TUC.
A UK Uncut spokesman said: "We have a right to protest and a right to be angry about the cuts. It is the use of force by the police which should be concerning people."
Spokesmen for the various retailers and banks named as targets by the group refused to comment on their security arrangements. A spokesman for Tesco said: "At £1.3bn, Tesco's tax contribution is among the highest in the country. Together with the £1.9bn we collect on behalf of the Government in national insurance and VAT, we bring more than £3bn to the Exchequer."