The last British resident held at Guantanamo Bay is set to take legal action against the Government following his release, sources said.
Shaker Aamer is marking his first full day of freedom back in Britain after being held for 13 years without charge at the US military facility in Cuba.
It is understood the father of four, who is receiving treatment in hospital, has already been reunited with his wife Zin.
He is due to meet his children this weekend, including youngest son Faris, who was born on the same day Mr Aamer arrived at Guantanamo.
Mr Aamer is now expected to bring legal proceedings against the British Government over its alleged complicity in his mistreatment.
A source said: "Proceedings were initiated some years ago on his behalf that could not be followed until his return to the UK.
"They will now, undoubtedly, be progressed."
Reports that Mr Aamer could be in line for a compensation payout in the region of £1 million were "speculation", the source added.
Clive Stafford-Smith, of human rights group Reprieve, said it was a "huge priority" for Mr Aamer that claims of UK complicity in rendition and torture are investigated.
He told BBC Breakfast: "We had a promise from the Prime Minister that there would be a fully independent inquiry into all of this torture. Unfortunately that's not happened yet.
"This is a huge priority of Shaker's. He doesn't want to have people persecuted. He doesn't want to have small people, who were sent out to do their jobs, prosecuted for what they did.
"What he does want is that the whole world should know what did happen so we can set in place rules so that British agents and, let's hope, American agents don't get involved in the torture business in the future."
Mr Aamer is suffering from a number of medical conditions including post-traumatic stress disorder, one of his lawyers, Ramzi Kassem, told BBC Radio 4's Today programme.
After returning to the UK, Mr Aamer paid an emotional tribute to those who fought for his release, saying: "Without their devotion to justice I would not be here in Britain now."
The 46-year-old arrived on a private plane at Biggin Hill airport in south-east London yesterday afternoon.
Mr Aamer has said he was originally seized by bounty hunters while working as a charity worker in Afghanistan in 2001 shortly after the 9/11 attacks.
The Saudi national was handed over to US forces and in February 2002 he was transferred to Guantanamo Bay and accused of aiding al Qaida.
But in 2007 the allegations against him were dropped and he was cleared for release.
Despite a formal request by then foreign secretary David Miliband, American authorities refused to allow him to go.
During his time in captivity, Mr Aamer's lawyers said he was tortured and held in solitary confinement for 360 days. In 2005, he lost half his body weight during a hunger strike.
Saeed Siddique, his father-in-law, said justice had been done - "but too late" - and Mr Aamer had already been offered compensation during the latter stages of his detention.
Former hostage Terry Waite, who was held captive for 1,760 days after going to Beirut in 1987 , urged Mr Aamer to withdraw from public view for a while.
Mr Waite told Today: "He has suffered a grave injustice. Whatever the background, to keep someone for 13 years without charge is really beyond the pale.
"The best thing is for him to withdraw for a while to get the treatment that's necessary."