David Shayler

People working for Britain's secret services who break their code of silence can expect no mercy, Tony Blair has warned.

In the wake of the jailing of David Shayler, the prime minister has said that spies who reveal classified secrets must face "the full force of the law".

On Tuesday former MI5 agent Shayler was sentenced to six months in jail after being found guilty of breaking the Official Secrets Act by revealing details of intelligence operations to a national newspaper.

Speaking during prime minister's questions on Wednesday, Tony Blair indicated he had no sympathy with Shayler's defence.

The ex-intelligence officer had sought to win the right to defend is actions on the grounds of public interest.

And his position was supported by Labour backbencher Vera Baird, who urged the prime minister to consider allowing a public interest defence for anyone who discloses information on unlawful activities by the security services.

"I'm making no comment about Shayler's case at all, but wouldn't a carefully drafted public interest defence offer a sensible extra means of control over the intelligence community and at the same time the protection for people of conscience by allowing the jury to balance whether on the whole the public has benefited or been harmed by a disclosure," she said.

Blair rejected the call.

"It is absolutely right that we make it clear that people who work for our security services undertake certain obligations of confidentiality," he told MPs. "There is really no way we could protect our country properly otherwise."

"I think particularly in these troubled times it must be very, very clear to people - I won't comment on the individual case - that if they work for the British security services they abide by their conditions of employment and confidentiality, and if they don't I'm afraid they will face the full force of the law."