Supporters of Sheikh Raed Salah, the head of the Islamic Movement in Israel, say he had entered the UK legally [EPA]

Sheikh Raed Salah, the leader of the Islamic Movement in Israel, who is being detained by British authorities will face a court hearing on Friday.

Salah was arrested and detained last Tuesday for allegedly entering the country illegally.

Salah, deemed to be widely respected as a leader of Israel's 1.3 million Arabs, was to take part in a speaking tour on the plight of Palestinians living in Israel.

He had been arrested by Israeli police a number of times earlier, and been periodically banned from entering Jerusalem. He also previously made headlines by spending two years in an Israeli prison for allegedly raising money for Hamas.

Israeli ministers have called for the outlawing of his wing of the Islamic Movement, which boycotts Israeli parliamentary elections for its refusal to recognise an exclusively Jewish state of Israel.

An immigration court will decide in a hearing on Friday whether to allow him to stay in the UK or have him sent back to Israel.

Salah's organisation, however, insists that he entered the UK through formal and legal channels and had no knowledge of any travel ban.

Salah was transferred from an immigration detention centre to a formal prison last Friday.

Theresa May, Britain's interior minister, said in a statement to Al Jazeera that an investigation was under way into how Salah had been able to enter the country.

"We do not normally comment on individual cases but in this case I think it is important to do so," May said.

The interior ministry said there was a ban order on Salah, but would not confirm when or why it was imposed.