They also plan to travel to America in the spring to draw more attention to the cases.
"Our hope is to speak as directly and simply as possible... to the American conscience, to say that human rights law, humanitarian law, must be applied to these 660 young men" held at the US Naval base, said actor Corin Redgrave.
Redgrave and his sister Vanessa were among the public figures announcing the formation of the commission at the House of Commons on Tuesday.
"All we are asking is that the Guantanamo prisoners are given their basic human rights as prisoners of war", Redgrave stressed.
Hopes were raised earlier this month that some of the British detainees may be released shortly when a senior US official reportedly said seven of them would be repatriated if the UK "managed them".
American Civil Liberties Union President Nadine Strossen said her group would work with the commission to seek redress for the detainees, who had been held for as long as two years without charge or access to lawyers.
With the help of the Guantanamo Human Rights Commission, my country would be true to what it said on paper," Strossen said, arguing that the detentions violated the US Constitution.
She and others expressed hope the US Supreme Court would rule that Guantanamo prisoners could challenge their detention in America's civilian federal courts.
"No government can put itself outside or above the law or we have a reign of lawlessness," said Vanessa Redgrave. "We cannot fight terrorism that way, we will explode terrorism that way."
Azmat Begg, father of a detainee
says not enough is being done
American authorities say the detainees are suspected al-Qaida and Taliban fighters whose interrogations have provided intelligence crucial to anti-terror efforts.
Azmat Begg, the father of detainee Moazzam Begg, called the detentions unjust and said he was deeply disappointed with what he said was the British government's failure to help.
"We call ourselves the mother of civilization, we call ourselves champions of democracy, but what we are doing, we can see it ourselves," he said.
Zumrati Juma, the mother of detainee Feroz Abbasi, also said Britain had not done enough to help resolve the prisoners' status.
Nine British citizens are among the Guantanamo detainees.
Rights groups have condemned
the treatment of detainees
Representatives of some of the six French detainees also attended the new commission's news conference.
Prime Minister Tony Blair said recently he expected the British detainees' legal status to be resolved within weeks, but warned they would not be brought home if they posed a terror risk.
Last week, 175 British legislators filed a brief in the US Supreme Court case on behalf of the detainees.
Human rights scandal
International human rights groups have slammed the detention and activities at the camp.
"The treatment of the Guantanamo detainees is a human rights scandal which violates international law and damages US claims to uphold the rule of law," Amnesty International said in a statement.
Human Rights Watch also says at least three children between 13 and 15 years of age have been held for more than a year at Guantanamo, where an uncertain number of 16 and 17-year-olds are also jailed alongside adults – in contravention of international law.