Police swooped on a protest organisation
Jonathan Blair, 38, from Newport, Daniel MacQuillan, 35, and Richard Moth, 32, from north London, left the police station in Pavia, northern Italy, where they were being held.
The Foreign Office says none has been charged with any offence
Mr McQuillan was among a group of people who were detained during an allegedly brutal police raid on Saturday night.
An Italian judge had ruled the arrests of 90 protesters illegal after no one had been allowed to contact their families, lawyers or consular officials, Mr McQuillan's lawyer Gilberto Paganni said.
Mr Paganni said he was "astonished" at Mr MacQuillan's treatment by officers who refused to allow him to make a single phone call while in custody.
"I have never seen something like that in my professional life," he said.
Mr Paganni called the incident "a suspension of constitutional guarantees in our country".
There were complaints from relatives and campaigners when four of the demonstrators were not allowed to see consular staff or lawyers after they were seized in a raid on the headquarters of a major protest group.
There are also allegations police used excessive force during the arrests.
Diplomats were finally granted access earlier on Wednesday after the five had been seen by an examining magistrate.
UK authorities criticised
The anti-capitalist group to which some of the protesters belonged has claimed the UK authorities have been ignoring the five to keep them out of the public eye.
Two other Britons arrested during the summit, Lawrence Miles, 25, and John Colin Blair, 19, originally from Ballymena, Northern Ireland, had earlier been freed by police.
Jonathan Neale, of Globalise Resistance, the anti-capitalist group to which the pair belonged, said they had been further beaten while in police custody and that pressure was being exerted "from on top" to keep them out of the public eye.
Foreign Secretary Jack Straw said Mr Neale's claims of further beatings would be investigated.
He told BBC Radio 4's Today programme: "If there are allegations of assault they of course need to be investigated."
Mr Neale also claimed the orders to leave the couple in limbo had come from Prime Minister Tony Blair in a bid to back his own stance on the riots.
The Foreign Office dismissed the claim as "rubbish".
Miss Doherty's parents have supported allegations by the solicitor for their daughter and Mr Moth that they had been assaulted by police and denied consular access.
However, Italian authorities have defended the actions of the police, who, they said, were faced by a section of protesters intent on provocation.
The couple were arrested with 88 other people when police swooped on the Genoa Social Forum (GSF) on Saturday night after two days of anti-G8 summit rioting.