Ministers have announced proposals to tighten up the regulation of undercover police following a succession of scandals over the infiltration of protest groups.
Damian Green, the minister for policing, told MPs on Tuesday that under the plans to be brought before parliament the police spies would be deployed only following approval from an outside body.
In a second reform, the use of the spies would only be authorised by chief constables. Previously, officers as junior as a superintendent had the power to deploy spies. The officers infiltrated political groups over many years.
The announcement of the new legislation follows a long-running Guardian investigation that revealed abuses by the spies in an undercover operation monitoring political campaigns since 1968.
The investigation showed that the undercover police routinely formed long-lasting, intimate, relationships with the activists they were sent to spy on. At least two police officers had children with activists while they worked undercover.
Police have also conceded that it was common practice for the agents to adopt the identities of dead children to develop their fake personas.
The controversy began two and a half years ago when the Guardian revealed details of the seven-year deployment of the police spy Mark Kennedy, who lived among climate change campaigners and who had several relationships with women upon whom he spied, one of which lasted six years.
Three senior judges later found that Kennedy might have acted as an agent provocateur.
Called before the home affairs select committee, Green said that any covert deployment lasting more than a year would need to be authorized by the office of surveillance commissioners, which monitors covert operations by state agencies.
The watchdog, led by the retired judge Sir Christopher Rose, has been criticised for failing to rigorously invigilate the use of many kinds of surveillance by government bodies, ranging from the police to local councils. Under the plans, the office would have to be notified before any operation was begun.
Green said: "Undercover police operations are vital in the fight against terrorism and serious organized crime. However, covert powers must be used proportionately and only when necessary."
He said the new measures would "provide enhanced judicial oversight of all undercover police deployments".
The proposed legislation brings into force proposals by Her Majesty's Inspectorate of Constabulary last year, in a report into Kennedy, who infiltrated environmentalists for seven years.
Sir Denis O'Connor, then chief inspector of constabulary, said the level of authority needed to deploy an undercover police officer for several years in a protest group was less than was required to plant a listening device in the car of a drug dealer.
Under present rules, a warrant from the home secretary is required for a wire tap, but police can take on new identities, living in the homes of their targets, with nothing more than a signature from a superintendent.
O'Connor described the discrepancy as surprising, and said "serious consideration" should be given to legislation that would make undercover policing as accountable as other forms of intrusive surveillance.