An illegal immigrant convicted of “revolting” sex offences is to receive damages after a judge concluded he was illegally detained by Home Office officials for around seven months.

Naseer Chawki, who claims to be 34 and from Iran, won a High Court fight with Home Secretary Theresa May following a hearing in London.

Deputy High Court Judge Stephen Morris said the size of the payout for Chawki would be assessed, and gave no indication what the figure would be.

Chawki, who had failed in a bid to claim asylum, claimed that he was held in immigration detention when then was “no prospect” of him being deported, and therefore his detention had been unlawful.

Mrs May disputed his claim. She said he had been found guilty of a serious crime and posed a “serious risk of harm” to the public, and there was a “serious risk” that he would abscond.

Lawyers told Judge Morris that Chawki arrived in Cardiff in 1999 before moving to Liverpool then Seven Sisters, north London.

In November 2008 he was given a three-year jail term after being convicted of two sex assaults and possessing a false identity document.

The sentencing judge, who heard Chawki had taken advantage of women on a crowded train, said the sex offences were “revolting” and had “very lasting effects” on the victims.

Chawki was placed in immigration detention following his release from jail in December 2009, after ministers ordered his deportation.

He was released from immigration detention in late March last year – but made to wear a monitoring tag – after attempts to deport him failed.

Judge Morris ruled that detention was lawful for the majority of the four years and four months Chawki was held, b ut he concluded that detention was unlawful between mid-September 2013 and late March last year.

He said by mid-September 2013 there had been “no sufficient prospect of removal within a reasonable time”.