The Metropolitan Police has repeated apologies for controversial tactics used by undercover officers as a public inquiry into the secret practices continues.

The latest series of hearings in the public inquiry into undercover policing began on Wednesday, looking at the activities of the force’s Special Demonstration Squad (SDS) between 1973 and 1982.

During the next three-and-a-half weeks, the inquiry will hear evidence on the first times that undercover officers had sexual relationships under their fake identities.

This was also the first time they were instructed to use aspects of the identities of dead children without their families’ consent.

In a statement released by the Met on Wednesday, Helen Ball, Assistant Commissioner for Professionalism, said the period included rioting and the start of the IRA bombing campaign in England.

Metropolitan Police Assistant Commissioner Helen Ball
Helen Ball said some actions were ‘unacceptable’ (PA)

She said: “It was against this challenging backdrop that the SDS were operating.

“In this part of the inquiry, evidence will also be heard about officers’ actions and behaviour, which in some instances were clearly inappropriate and unacceptable – certainly by modern standards, and in some cases by the standards of the time in which they occurred.

“The inquiry will hear examples of undercover officers entering into inappropriate sexual relationships with women they met during their deployments and of undercover officers using the identities of deceased children – a practice that does not happen now.

“The Met acknowledges that these cases caused significant harm and distress, and for this we are sorry.”

Witnesses including Piers Corbyn and Lord Peter Hain are expected to give evidence during the coming weeks.

Celia Stubbs, the partner of anti-racism campaigner Blair Peach who died after being hit over the head by a police officer during a protest, will also take part.

The Undercover Policing Inquiry
Piers Corbyn, who was spied on for nearly 20 years, is among the witnesses expected to give evidence (Jacob King/PA)

The Undercover Policing Inquiry (UCPI) was set up in 2015 to look at the activities of two shadowy police units after condemnation of undercover tactics.

A public outcry was sparked when it was revealed women had been tricked into sexual relationships with undercover officers and that police spies had used the identities of dead children without their families’ permission.

Family justice campaigns, including for murdered teenager Stephen Lawrence, were spied upon; and there are claims that some officers were arrested or prosecuted for crimes under fake identities, leading to alleged miscarriages of justice for their co-defendants.

The two units being examined are the Metropolitan Police’s Special Demonstration Squad (SDS), which existed between 1968 and 2008; and the undercover part of the National Public Order Intelligence Unit (NPOIU), which existed between 1999 and 2010.

The Undercover Policing Inquiry
Neville Lawrence, the father of Stephen Lawrence (right), and Stephen’s friend Duwayne Brooks, who were both spied upon by undercover police officers (Helen William/PA)

On Wednesday, counsel to the inquiry David Barr QC said the current batch of hearings will look at the deployment of 29 undercover officers, who on average were on assignment for three to five years.

The earliest was one using the cover name David Robertson between 1970 and 1973, and the latest who used the name Phil Cooper between 1979 and late 1983 or early 1984.

The inquiry will hear evidence from eight undercover officers in person, with written statements from another seven. Nine non-police witnesses will also give evidence, with three providing written statements.

Those giving evidence in person include Mr Corbyn, the brother of former Labour leader Jeremy Corbyn, who was spied on for nearly 20 years after he joined a squatting movement for affordable housing in 1971. He is due to give evidence on April 28.

Lord Hain was a leader of the anti-apartheid Stop the Seventy Tour campaign, which aimed to stop the all-white South Africa cricket team touring the UK in 1970, and to disrupt a tour by its rugby team in the winter of 1969/70. He is due to give evidence on April 30.

The mammoth inquiry has cost more than £36 million to date, although Tory peer Lord Moylan estimated last week that this could rise to £100 million, including police costs, by the time the inquiry reports in 2023.