The detainees left Libya after facing what it described as difficulties, state-run BBC reported on Sunday.
It said the British team, which arrived in Libya on Friday, was tasked to hold talks with opposition leaders.
Revolutionary forces said the British were carrying weapons, map and passports from four different countries, and were arrested because their identities were not known.
British media sources have reported that the members of Britain’s Special Air Service unit were in Benghazi on a secret diplomatic mission.
Though UK has loosened its long-time support for Libyan ruler Muammar Gaddafi because of the violent crackdown of people by his regime, the revolutionary National Council rejected the British delegation’s proposal for talks.
In response to US Secretary of State Hillary Clinton, who had claimed support for opposition forces in Libya, the council said it refused any foreign intervention in the country.
Meanwhile, the ongoing violence in Libya has become harsher. Gaddafi’s loyalists launched fresh aerial attacks in the oil-rich city of Ras Lanuf on Sunday to regain the control of the city from anti-regime forces.
Earlier in the day, Libya’s state TV claimed pro-Gaddafi forces had retaken control of Ras Lanuf, the western city of Misratah and the eastern city of Tobruk. Protesters rejected the claim, saying they are in full control of the cities.
Fighting has also broken out in the eastern city of Ben Jawad where 11 people including a French journalist were reportedly injured on Sunday.