The High Court has found that the Home Office acted unlawfully in a programme known as Project Sunshine in which data was extracted from mobile phones seized off migrants who arrived on small boats.

Immigration officers practiced a “secret and blanket policy” of seizing the phones, which was unlawfully carried out using immigration powers, the High Court ruled on Friday.

The judgment follows Sky News revealing the cases of approximately 850 individuals are being examined to see if the department broke privacy laws, which could result in a £17m fine.

It comes as the home secretary, Priti Patel, faces increasing pressure over small boat crossings in the English Channel which have risen exponentially despite her pledging to halve them.

More than 4,000 people have made the dangerous journey across the English Channel aboard small boats so far in 2022, around four times as many as this time last year.

More than 28,000 migrants were detected making the perilous journey from France to the UK last year – 37 of whom drowned, according to the International Organisation for Migration – and a forecast has suggested the figure will almost double to nearly 60,000 in 2022.

Among the court’s findings was that Immigration Officers lied to migrants by claiming that they could be prosecuted for not handing over their mobile passwords when in fact there was no such offence.

Clare Jennings of Gold Jennings, one of the lawyers who brought the case, said: “I am delighted that the High Court has today upheld the rights of the claimants, and the thousands of other asylum seekers like them.”

These people “committed no crime but who were nevertheless subjected to this blanket and secret policy of having to hand over their mobile phones and PIN numbers immediately upon arrival causing them significant emotional and practical hardship,” said Ms Jennings.

The “systematic extraction of personal data from vulnerable asylum seekers, who were not suspects in any crime, was an astonishing and unparalleled assault on fundamental privacy rights,” Ms Jennings added.

“Today’s judgment provided much needed clarification as to the extent of immigration officers powers of search and seizure and confirmed beyond doubt that the Home Secretary’s policy of seizing all mobile phones from small boat arrivals was unlawful.”

A Home Office spokesperson said: “Channel crossings are an overt abuse of our immigration laws but they also impact on the UK taxpayer, risk lives and our ability to help refugees who come to the UK via safe and legal routes.

“It is paramount that we continue to go after those facilitating dangerous crossings.

“We are considering the judgement and it would be inappropriate to comment further at this stage,” they added.