LONDON (REUTERS) - A British man who was once held at Guantanamo Bay will be freed from prison, police said on Wednesday, after prosecutors dropped accusations that he had attended a terrorism training camp in Syria a week before he was due to go on trial.

Moazzem Begg, 46, who became a high-profile human rights campaigner after being released without charge from the U.S. military prison in Cuba in 2005, had been held for seven months in custody on charges of facilitating terrorism and possession of a document likely to be of use to a terrorist.

His case is likely to pose awkward questions for the police and the government which has vowed tough action against those who travel to Syria, including stripping Britons of their passports.

Cage, a group set up by Begg which campaigns for the rights of people detained during counter-terrorism operations, had argued his arrest in March was politically motivated.

Begg, a vocal critic of British foreign policy, said he had been in Syria as part of research into cases of illegal rendition and torture involving Britain's security services. "I understand this is going to raise many questions," said Marcus Beale, Assistant Chief Constable of West Midlands Police.

He said new material had come to light which meant police and prosecution lawyers concluded there was no realistic chance of securing a conviction. "From the beginning this case has challenged the relationship between West Midlands Police and some of the communities we serve," Beale said in a statement. "I would like to reassure them and Mr Begg that at every stage of this investigation my officers acted in the best interests of the public and of justice." Begg's release comes a day after Home Secretary Theresa May said there would be a new counter-terrorism bill by the end of November which would give her more powers to strip Britons suspected of travelling to Syria and Iraq of their passports.

The authorities fear those who travel to the region could return radicalised and pose a risk on their return. May said she had already removed the passports of 25 people in relation to Syria while 103 had been arrested over offences related to terrorism there.