No charges will be brought over allegations of the rendition of two families to Libya 12 years ago.
There is "insufficient evidence" to press criminal charges as part of the investigation into how the Belhadj and Al Saadi families were handled, the Crown Prosecution Service said.
The CPS, working with the Metropolitan Police on the investigation known as Operation Lydd which was set up to consider complaints of ill treatment against detainees, looked at "a large number" or records, people and organisations including the security services and Government departments.
Abdel Hakim Belhaj and Sami al-Saadi, along with members of their families, were kidnapped and sent to face punishment in Libya in 2004.
Mr Belhadj and his wife, Fatima Boudchar accused former Foreign Secretary Jack Straw and an ex-senior MI6 officer, Sir Mark Allen, of being responsible for their forced return to Colonel Gaddafi's Libya in March 2004 where they suffered ill-treatment.
Sue Hemming, head of the CPS's Special Crime and Counter Terrorism Division, said: "Following a thorough investigation, the CPS has decided that there is insufficient evidence to charge the suspect with any criminal offence.
"We made our decision based upon all the available admissible evidence and after weighing up all of the information we have been provided with."
Mr Belhadj, a key military figure in the uprising that toppled Gaddafi who was living in exile in Beijing, China, said he was tortured after being detained with his wife en route to the UK where they were trying to seek asylum.
Following four years of investigation, the CPS said no charges will be brought.
On charges of aiding or abetting kidnap, the CPS found that, as the alleged offences took place abroad, it cannot prosecute in the UK, and it found there was not enough evidence to bring charges in relation to aiding or abetting torture.
It also found there was insufficient evidence to prosecute the suspect, who was not named, on the charge of misconduct in public office.
In its conclusions the CPS said: "There is sufficient evidence to support the contention that the suspect had:
"(a) been in communication with individuals from the foreign countries responsible for the detention and transfer of the Belhadj and Al Saadi families;
"(b) disclosed aspects of what was occurring to others within this country; and
"(c) sought political authority for some of his actions albeit not within a formal written process nor in detail which covered all his communications and conduct."
But the CPS said it "remains unclear" what impact the conduct of the suspect had on the actions of those making decisions abroad.
Cori Crider, a lawyer for the two families at international human rights organisation Reprieve, said the findings are "official acknowledgement that British officials were involved in this rendition".
Ms Crider said: "There is one crucial question: who knew who was on those planes, and for those who knew, what possible reason can there be for them to evade justice?
"Top British officials helped abduct a pregnant woman and four children, and so far, we have no apology, no explanation, and now no-one held responsible. Sir Mark Allen (ex-senior MI6 officer) took credit, in writing, for the operation. Jack Straw, we are told, signed it off. The head of MI5 was so incensed about all this she wrote to Tony Blair at the time.
"Strangely, the CPS's attitude to all this is 'See no evil, hear no evil, and speak no evil'. It is hard to escape the conclusion that this decision has a great deal to do with political power and very little to do with the rule of law. While these families have been denied justice at every turn, we are determined to keep fighting for it."
Mr Belhadj told the BBC: "The police investigation was very important. Justice should be independent. Politics should not interfere."