I did what I did because I love my country. I am not a traitor to it.

David Shayler

After saying goodbye to his family, who accompanied him on the trip, he was taken through a side entrance to a waiting police van.

Mr Shayler later arrived at Charing Cross police station, central London, in an unmarked car and was taken into the building by a side entrance, police confirmed.

He will either be released on bail after questioning or held at Belmarsh prison in south east London.

'Scandalous'

Speaking immediately after his arrest, Mr Shayler's girlfriend Annie Machon said: "I find it scandalous that he can be arrested and taken for questioning, and yet all he has done is tell the truth."

His mother Anne Shayler said it was a very emotional experience to have him back in the country. She added: "I'm very proud of him. My first reaction was - someone had to do this but why does it have to be my son?"

Annie Machon said he would be "vindicated"

Mr Shayler is expecting to be approached by separate officers over his allegations that MI6 agents plotted to kill Libyan leader Colonel Gaddafi - interest that he says justifies his whistleblowing campaign.

The row is the biggest the UK Government has faced over revelations within the security services since the Spycatcher affair in 1986, in which the government tried to suppress publication of the memoirs of former spy Peter Wright.

In the light of Mr Shayler's recent reiteration of his claims about an MI6 plot, the Foreign Office said it had already made its position on the allegations clear, and had nothing to add or subtract.

Mr Shayler has been living in "political exile" in Paris for three years after making a string of allegations about the British secret services.

It is understood he will face two charges, which carry a maximum four years in prison, following his arrest.

'Assassination plot'

Before his departure Mr Shayler said he would face a criminal trial because he believed he had done nothing wrong.

He said: "I did what I did because I love my country. I am not a traitor to it.

"I knew about crime, the MI6-funded plot to assassinate Colonel Gaddafi, but I couldn't take that anywhere," he told the BBC. "If I had done, I'd be committing a crime myself."

He said the police investigation into the alleged Gaddafi plot, which left several civilians dead, proved he was right to leak details to the press.

Mr Shayler said the two MI6 officers he claims were involved should be tried for conspiracy to murder.

"It is a disgrace in this country that the government continues to collude with MI6 to prevent two officers being brought to justice for their part in conspiracy to murder. That is an abuse of power," he said.

'Flawed and archaic'

Mr Shayler believes a new human rights law - the European Convention of Human Rights - due to be incorporated into British law on 2 October will help his cause.

He said: "I don't think the government really wants me in court. The government has always misled and lied to the British public in my case and I would be seeking disclosure of documents to prove that in any trial.

"In those circumstances I think the government would rather drop the prosecution.

"Even if convicted, Britain will still have a prisoner of conscience in its jails. I just acted on conscience."

Andrew Mackinlay, who is challenging for the chairmanship of the Parliamentary Labour Party, said ministers risked making themselves look silly if Mr Shayler was charged under the "flawed and archaic" act.

Liberal Democrat home affairs spokesman Simon Hughes said there was growing support for the reform of the Official Secrets Act, which bars Whitehall officials and military staff from revealing sensitive information.

But Armed Forces Minister John Spellar said it was essential to maintain the security of the intelligence agencies.