A police spy appears to have misled a public inquiry about sexual relationships he had with two women while he was undercover.

The undercover officer initially told the inquiry he had not had sexual relationships with the two women while using the fake name of James Straven.

He later admitted to having the relationships while he infiltrated animal rights groups between 1997 and 2002. The two women only discovered he had deceived them after he made this admission.

A public inquiry, led by the retired judge Sir John Mitting, is examining the conduct of undercover officers who spied on more than 1,000 political groups since 1968. One of the issues it is due to look at is how the police spies frequently formed intimate relationships with women while concealing their real identities.

According to the inquiry, Straven denied the existence of the two relationships in a signed statement in October 2017. At that time, he had for more than a year been attempting to persuade the inquiry to make a legal order keeping his identity secret.

However, in April 2018 he admitted he had had intimate relationships with both women, according to the inquiry.

The women have now become part of the inquiry and are due to give evidence about how he deceived them.

One of the women, known as Sara as she has been granted anonymity by Mitting, has told the inquiry that Straven conducted a deceitful intimate relationship with her between late 1998 and March 2001.

Sara said: “Why should we be surprised that he hasn’t been honest? Anything any undercover officer has to say is up for argument – they are trained liars and deceivers.

“Apart from the confusion and deep emotional effects of these officers on the women targeted, what appals me is that these relationships appear to have been sanctioned at a higher level, which amounts to state abuse and institutionalised sexism. No concern at all for using women’s lives, including the wives of the officers.”

The second woman, known as Ellie, has told the inquiry that in 2001, Straven had initiated a sexual relationship with her that lasted about a year.

Straven lost his attempt to keep his identity concealed as Mitting did not accept his denial about the sexual relationships.

Straven said he “intends to fully cooperate with the inquiry and will provide any evidence he is able to give to the inquiry and it does not seem appropriate that matters the inquiry is going to investigate should be ventilated in the media beforehand”.

The inquiry was set up in 2014 by the then home secretary, Theresa May, after what she called “serious failings” in undercover policing had been exposed. The inquiry – which has been much delayed – is due to start hearing evidence in public in June.

An analysis by the Guardian shows that so far, 20 undercover officers deployed in political groups between the mid-1970s and 2010 are known to have had sexual relationships, some of them lasting years, while using fake identities. All but one are men. Some of the men had relationships with more than one woman during their undercover missions.

Police have paid compensation to at least 12 women who were deceived by undercover officers who spied on political groups.

Straven was a member of the Metropolitan police’s special demonstration squad (SDS), which infiltrated political groups between 1968 and 2008. He spied on the Animal Liberation Front and a group of London activists from Brixton and Croydon who opposed foxhunting.

Mitting’s inquiry is also examining why Straven appears to have used a second false identity while undercover, without the authorisation of his SDS supervisors.

According to the inquiry, this second identity was Kevin Crossland, a five-year-old boy who had died in a plane crash in the former Yugoslavia in 1966 when going on holiday with his family.

Undercover officers routinely stole the identities of dead children but did so with the authority of their superiors.