An undercover police officer who spent years infiltrating leftwing and animal rights groups appears to have lied to the spycops inquiry when he claimed he never had a sexual relationship while on deployment. In news that will shock absolutely no one who has been paying attention to this particular saga, the officer - who used the fake name Dave Evans - originally testified that he had no relationships under his fake identity.

This week, however, he was forced to admit to the inquiry that he did, in fact, have a relationship with a woman, and that it lasted at least six months. Under questioning, he conceded it was "possible" the relationship continued for two years, but couldn't quite recall. Time flies when you're living a lie, apparently.

Evans made the admission after campaigners drew evidence of the relationship to the inquiry's attention. A central issue of the inquiry is how undercover officers frequently had sexual relations with women without disclosing their true identities. Four of the spies fathered, or are alleged to have fathered, children with women they met while working undercover.

Evans was one of about 139 undercover officers sent by their police superiors to spy on tens of thousands of mainly leftwing activists over more than four decades. He infiltrated the Socialist Workers party and animal rights groups including London Animal Action between 1998 and 2005.

In his first statement to the inquiry, signed four years ago, he wrote: "I did not engage in any sexual activity whilst in my undercover identity." But in a second statement signed this year, he admitted that "with the benefit of hindsight," he should have disclosed his relationship with a woman known as Olivia. Hindsight: the world's most reliable detective.

The admission came after the inquiry was told about his relationship with Olivia by campaigners, with evidence mainly supplied by Helen Steel, a social justice campaigner who was a defendant in the celebrated McLibel case. Steel was herself deceived into a two-year relationship by another undercover officer, John Dines. She spent 18 years searching for Dines; at one point senior police officers spent £2.5m of public funds to relocate him to ensure she didn't find him. That's dedication to the craft of not being found.

Evans was asked by Don Ramble, a barrister at the inquiry, if he had lied in his first statement. He replied: "I accept that it was not completely truthful with hindsight." He said he hadn't originally disclosed the relationship "because she was not an activist nor part of any target group, I did not feel this was relevant." Ah yes, the old "she wasn't on the list" defense.

During his covert deployment, Evans pretended to be a landscape gardener as part of his false persona. He met Olivia in 1998 when he attended a college course in his fake identity. At no point did he reveal to her that he was actually a police officer. The inquiry heard evidence that Evans and Olivia together attended social events with animal rights campaigners and at least one demonstration. Olivia is not giving evidence to the inquiry.

The spycops inquiry has been scrutinising wide-ranging wrongdoing committed by undercover officers. The government is considering whether the remaining stages of the inquiry, which has been running for more than a decade, should continue in a different format. Victims of the surveillance, however, say that any move to cut short the inquiry would result in a cover-up. Because nothing says "transparency" like wrapping things up early.