Plane-spotter Paul Coppin was the trip organiser
The 11 men being held in Nafplion prison attended a registration office in the town before boarding a bus to Athens on Friday afternoon.
The sole woman in the group, 51-year-old Lesley Coppin, was also released from her jail at Korydallos near Athens.
BBC correspondent Paul Wood said that once home, the group's lawyers believe the charges could simply melt away after being reduced from felony to misdemeanour level.
Red tape
Two of the 12 Britons, as well as two Dutch plane-spotters also being held, were the first to be freed on Friday morning after spending 37 days in jail.
It is understood the remaining nine men were then later allowed to leave Nafplion jail in groups of three.
After his release, trip organiser Paul Coppin said: "It's interesting to see another side of Greece other than a jail."
Peter Norris, 52, of Uxbridge, west London, said: "I am just so relieved. It has been an unbelievable few weeks and I still cannot believe we were arrested. The whole thing has been ridiculous."
The entire group spent Friday morning getting through red tape, after raising the required £9,000 bail.
"Each have had to fill out a mountain of paperwork - some reports say 12 separate forms each," he said.
Labour East MEP Richard Howitt, who has been campaigning for the group and visited the men on Friday morning, said they were in high spirits but still "very angry".
Delayed return
British embassy officials arrived at the jail earlier on Friday, after confirming the £9,000 surety for every defendant had been raised.
It is thought many of the group were paid the money by a national newspaper, which also provided the bus to transport them from jail.
Later on Friday, families back in England welcomed the news of their release and said there would be celebrations over the weekend.
Adele Yon, sister of Andrew Jenkins, 32, said: "It is the day we have all been waiting for. I can't wait to see him."
A spokeswoman for the Foreign Office said: "This is very good news and we are glad all 12 have been released together and will be back for Christmas.
"We will speak to them on their return and continue to offer support."
The group were arrested on 8 November at a Greek air show for allegedly illegally taking photographs.
They had faced a charge of spying, which carries a 20-year sentence, but this was reduced to misdemeanour charges of illegal information collection, which carry a five-year maximum.
But the defence lawyers understand that if the plane-spotters leave Greece quietly and do not threaten any legal action of their own, the case may either be dropped or "not guilty" verdicts will be returned.
The 12 British plane-spotters are:
The Dutch plane-spotters are Patrick Dirksen, 27, from Eindhoven and Frank Mink, 28, from Den Helder.