Foreign Secretary David Miliband said his release was the first step towards the goal of closing down the Guantanamo Bay detention camp.
After he landed at 1300 GMT and walked to the terminal building surrounded by officials, he was questioned and released more than four hours later.
UK Border Agency officials are interviewing him about his resident status and he will have to apply for leave to enter the UK.
The Home Office said he would be given temporary admission until a decision is made.
Mr Mohamed said in a statement: "I have to say, more in sadness than in anger, that many have been complicit in my own horrors over the past seven years.
"For myself, the very worst moment came when I realised in Morocco that the people who were torturing me were receiving questions and materials from British intelligence."
He had been accompanied by a doctor during his flight and said he was neither physically nor mentally capable of facing the media on the moment of his arrival back to Britain.
"I have been through an experience that I never thought to encounter in my darkest nightmares," he said.
"Before this ordeal, torture was an abstract word to me. I could never have imagined that I would be its victim.
"It is still difficult for me to believe that I was abducted, hauled from one country to the next, and tortured in medieval ways - all orchestrated by the United States government.
"While I want to recover, and put it all as far in the past as I can, I also know I have an obligation to the people who still remain in those torture chambers.
"My own despair was greatest when I thought that everyone had abandoned me. I have a duty to make sure that nobody else is forgotten."
Referring to his alleged period of torture in Morocco, Mr Mohamed said: "I have met with British intelligence in Pakistan. I had been open with them. Yet the very people who I had hoped would come to my rescue, I later realised, had allied themselves with my abusers."
He went on: "I am not asking for vengeance; only that the truth should be made known so that nobody in the future should have to endure what I have endured."
A Foreign Office spokesman said allegations British officials were complicit in his alleged torture were currently being examined by the Attorney General.
He also stressed the allegations were raised with the US authorities a year ago. "Discussions were the US authorities are ongoing," he added.
Mr Miliband said he was pleased Mr Mohamed was returning.
"His release and return from Guantanamo Bay is the result of a number of years of very hard work by officials with him and with his team," he said.
"Obviously, the release of Binyam Mohamed is the first release from Guantanamo Bay since the election of President Obama.
"We very much welcome President Obama's commitment to close Guantanamo Bay and I see today's return of Binyam Mohamed as the first step towards that shared goal."
Lawyer Clive Stafford-Smith reads a statement on Binyam Mohamed's behalf
Mr Mohamed's brother, Dr Benhur Mohamed said: "I'm very happy about his release. I am so excited today, it is the best day of my life.
"What happened under the US, it's very disheartening to know that the British actually had something to do with this suffering."
The Met Police said Mr Mohamed had been detained at RAF Northolt under border regulations, but had not been arrested.
Clive Stafford Smith, director of legal charity Reprieve which represented Mr Mohamed, said: "He is a victim who has suffered more than any human being should ever suffer.
British Prime Minister Gordon Brown refused to discuss the details of any restrictions on Mr Mohamed, but said: "We will do everything in our power to protect the security of people in our country and the home secretary will take whatever action is necessary."
The US had accused Mr Mohamed of involvement in a plot to detonate a "dirty bomb" in America, but the charges were dropped in October last year.
The US Department of Justice said in a statement on Monday that his release was "consistent with the national security and foreign policy interests of the United States and the interests of justice".
"The friendship and assistance of the international community is vitally important as we work to close Guantanamo, and we greatly appreciate the efforts of the British government to work with us on the transfer of Binyam Mohamed," Attorney General Eric Holder said.
Some 250 inmates remain at the US camp in Guantanamo
Mr Mohamed had lived in the UK from the age of 15, before being arrested in Pakistan in 2002.
Earlier this year he went on a month-long hunger strike at Guantanamo and his legal team said he was "close to starvation".
But last weekend he was declared well enough to travel back to the UK by a team of British officials who had visited him.
His lawyers insist he poses no risk to the UK.
One other UK resident, Shaker Abdur-Raheem Aamer, remains in Guantanamo Bay after being detained in Afghanistan in 2001.
Two other Guantanamo inmates claim to have been living in the UK prior to their detention, but those claims are disputed.
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