An Islamic political activist arrested after entering Britain has won the right to seek damages after a High Court judge ruled that his detention had been partially unlawful.

Sheikh Raed Salah was initially detained in London in June after a series of Home Office blunders allowed him to bypass immigration officials, despite being banned from the country.

Lawyers believe the 52-year-old father-of-eight could now receive thousands of pounds in compensation.

Home Secretary Theresa May imposed a ban on the grounds that Sheikh Salah's presence in Britain "would not be conducive to the public good". The Home Office levelled four allegations of antisemitism against him, all of which he has repeatedly denied.

It is alleged that he wrote a poem which included derogatory remarks about Jews, promoted martyrdom, invoked a blood libel, and made reference to the Protocols of the Elders of Zion.

Sheikh Salah's lawyers claim that the quotes were doctored by the Israeli media and strenuously deny their client has ever made antisemitic comments.

Home Office and Border Agency failures meant he was able to travel to Britain and begin a speaking tour in June.

When immigration officers eventually arrested Sheikh Salah at his west London hotel shortly after 11pm on June 28, they spoke in English and failed to explain the reasons for his detention to him in a language he could understand.

During the journey to the police station, one immigration officer used a translation application on his iPhone in a failed attempt to explain to Sheikh Salah what was happening.

In his judgment, Mr Justice Nicol said: "What took place at the hotel was inadequate for the claimant's arrest to be lawful. The claimant was entitled to know, at least in the broadest terms, why he was being arrested. Even in English that information was not conveyed to him. That alone meant the arrest was unlawful.

"I have accepted his argument that he was not given proper and sufficient reasons for his arrest on June 28, nor was he given them until some time on June 30. He is entitled to damages for wrongful detention during that period."

But the judge rejected Sheikh Salah's claim that the duration of his detention was not in line with government policy and was therefore unlawful.

A Home Office spokesman said: "We are pleased that the court has found that the Home Secretary used her powers correctly. The court decided that there was a technical problem when Mr Salah was initially detained."

Sheikh Salah's full deportation hearing is ongoing. It will decide whether he should be forcibly removed from Britain.

The Guardian claimed last week that Mrs May had acted to ban Mr Salah, leader of the northern branch of the Islamic Movement in Israel, shortly after the Community Security Trust presented officials with a report on his alleged statements.

The paper said Border Agency officials had warned the Home Secretary against barring him because the quotes were disputed and the possibility of a legal challenge from him if detained.

An initial online version of the Guardian story appeared to suggest CST had doctored the quotes before passing them to the Home Office. Following a complaint from CST, the Guardian clarified that these were the claims of Sheikh Salah's legal team and that there was no evidence to suggest CST had acted improperly.

Officials missed six opportunities to detain Sheikh Salah during his journey to London. The failures – both at Heathrow and Tel Aviv's Ben Gurion Airport – have not been revealed, but are known to include immigration officers at passport control in London missing an alert about Sheikh Salah's banned status.