John Wadham: David Shayler's lawyer

Mr Wadham said that allegation would not form part of the case against his client.

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?"

The David Shayler 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.

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

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.