Scotland Yard stands accused of covering up "institutionalised sexism" within the police in trying to block civil claims launched by women allegedly deceived into sexual relationships with undercover officers.

Police lawyers are applying to strike out, on secrecy grounds, the claims of five women who say they were duped into intimate long-term relationships with four undercover police officers working within the special demonstration squad (SDS), a Metropolitan police unit set up to infiltrate protest groups.

The legal bid, funded by the taxpayer, is being fought despite widespread outrage and promises of future transparency by Scotland Yard, following official confirmation last week that an undercover officer was deployed 21 years ago to spy on the grieving family of murdered teenager Stephen Lawrence.

The Observer understands that police lawyers are asking the high court to reject claims against the Metropolitan police on the grounds that the force cannot deviate from its policy of neither confirming nor denying issues regarding undercover policing.

It is understood that Scotland Yard will say in a hearing, scheduled to be held on 18 March, that it is not in a position to respond to claims and therefore cannot defend it.

Last week an independent inquiry revealed that an officer identified only as N81 was deployed in a group "positioned close to the Lawrence family campaign". The spy gathered "some personal details relating to" the murdered teenager's parents. It was also disclosed that undercover officers had given false evidence in the courts and acted as if they were exempt from the normal rules of evidence disclosure.

A separate report on a police investigation into the SDS found that three former officers who had had sexual relations with women who had not known their true identities could face criminal charges.

Harriet Wistrich, a lawyer at Birnberg Peirce & Partners representing the women, said it was absurd that Scotland Yard claimed to be transparent while blocking her clients' bid for justice in open court. On Friday the former director of prosecutions, Lord Macdonald, accused the police of engendering a "culture of conceit".

Wistrich said: "They should just hold up their hands and say, 'this is terrible, we recognise that and are doing everything we can do to put it right'."

Wistrich said Scotland Yard had made no move to reverse its legal position despite calls by Theresa May, the home secretary, for transparency in the wake of what she last week described as "profoundly disturbing" findings.

"They are basically saying that we have this policy and we have to uphold the policy because we gave lifelong assurances that we would not reveal their identities. This is nonsense when some have confessed themselves to being undercover officers.

"In total, we have got five different officers between the eight claimants and our own evidence suggests there was a deliberate kind of encouragement to do this. We are not just talking about a bad apple … but a rotten-to-the-core, institutionalised sexism."

The officers accused of forging long-term sexual relationships with women while undercover are Jim Boyling, Bob Lambert, John Dines and Mark Jenner.

Last week May announced a public inquiry into the work of undercover police officers shortly after the publication of the inquiry on allegations of spying on the Lawrence family.

There are additional calls, including by shadow business secretary Chuka Umunna, for an examination of the role of undercover officers in providing information for a blacklist operation run by major companies within the construction industry which forced more than 3,000 people out of the sector.

Brian Richardson, a barrister who has set up an umbrella group, Campaign Opposing Police Surveillance, said: "It is extremely important that the proposed inquiry considers the infiltration of the Lawrence family campaign and that of [all] the targets of police surveillance. However, we must continue to campaign to ensure that the inquiry is fully transparent and that those responsible … are held to account."