A 21-year-old man was wrongly convicted and fined £60 under new coronavirus laws, Britain's largest police force has admitted.
The case of a 15-year-old boy, who was also charged under the Coronavirus Act 2020, is being reviewed by the Crown Prosecution Service (CPS).
The PA news agency raised concerns with the Metropolitan Police about how the law had been applied in cases identified in an analysis of available London magistrates' court lists.
UK civil liberties group Big Brother Watch said it was "astonishing" the legislation is still being misused.
The Coronavirus Act, which came into force last month, allows officers to remove or detain a "suspected infectious person" for screening and assessment with "reasonable force" if necessary.
Police were given separate powers to break up gatherings and fine people breaching restriction of movement rules under the Health Protection Regulations 2020.
A 21-year-old man, who PA has chosen not to name as he faces outstanding charges, was arrested outside Tooting Leisure Centre on Saturday March 28.
He was later charged with possession of Class B drugs, going equipped to steal and acting contrary to paragraph 23(1)(a) and (2) of schedule 21 to the Coronavirus Act.
He pleaded guilty to all offences two days later at Wimbledon Magistrates' Court and was fined £200 for possession of drugs and £60 for the offence under the Coronavirus Act.
When first contacted about the case, the Met said it was not being reviewed but after further questioning last week, the force admitted: "It was identified this legislation had been applied incorrectly.
"The charge and fine were subsequently set aside. The charges for possession of Class B drugs and going equipped to steal were not overturned and the £200 fine stands.
"In this case officers were rightly dealing with an individual suspected of a separate crime and who was also in a public space without a valid reason.
"However, (he) was incorrectly charged with an offence under the Coronavirus Act 2020. This legislation only relates to 'potentially infectious persons' which was not applicable in these circumstances.
"This is very new legislation and we have been working with all of our frontline officers to help them interpret and understand it. This includes sharing the recent guidance from the National Police Chiefs' Council and the College of Policing.
"The officers involved have been spoken to and reminded of the way the legislation should be applied."
It comes after Marie Dinou, 41, was wrongly fined £660 under the legislation after she was arrested at Newcastle Central Station by British Transport Police.
Silkie Carlo, director of Big Brother Watch, said: "It's astonishing that after a string of damaging failures the emergency legislation is still being misused.
"These sweeping powers to fine and detain people are so broad that police may try to apply them to any one of us.
"We are in truly dangerous territory with such expansive powers and the police's inability to use them adequately is severely damaging public trust as well as the rule of law."
The Met said another case, involving a 15-year-old boy, was being "re-examined" by the CPS.
The teenager was arrested in Kingston, south-west London, on Thursday April 2 and later charged with possession of a bladed article in a public place and failure to comply with a restriction contrary to paragraph 23(1)(a) and (2) of schedule 21 to the Coronavirus Act.
He pleaded not guilty to the charges at Wimbledon Magistrates' Court the following day and is due back before the same court on May 6.
A CPS spokesman said: "We keep cases under review and that will be considered at the next hearing."
The spokesman said no figures were yet available on the number of charges brought under the Coronavirus Act or how many were being reviewed.
The Met said there was no issue with the case of Petru Nedea, 31, who had been listed on court documents as having been charged under the Coronavirus Act.
A Wimbledon Magistrates' Court official said he was let off without punishment after the charge was changed to an offence of breaching a restriction of movement requirement under the Health Protection Regulations.
Hassan Adnan, 33, appeared at Westminster Magistrates' Court on Wednesday charged under the Coronavirus Act and with a count of common assault of a police officer.
The court heard Adnan, of no fixed abode, was with a group of others in the borough of Westminster when he coughed towards a police officer and refused to leave the area as instructed.
He pleaded not guilty to both charges and is due to appear at Southwark Crown Court on May 6 over the alleged assault, while the other matter will be dealt with at the magistrates' court in August.
Warwickshire Police said Robert Grant, 27, from Nuneaton has been charged with failure to comply with a restriction imposed under Coronavirus Act and drink driving and aggravated vehicle taking following a collision in Bedworth last week.
He is due to appear at Warwickshire Magistrates' Court on May 18.
PA has asked whether the cases of Adnan and Grant are being reviewed.