One of Britain's spy chiefs has rejected suggestions that the work of the security and intelligence services was compromising freedom and democracy in the UK.

MI5 director general Andrew Parker told a parliamentary committee that the £2 billion (€2.4bn) annual budget of the agencies was "proportionate" to the threats facing Britain and its way of life.

Mr Parker was appearing alongside MI6 chief John Sawers and Iain Lobban, the director of GCHQ, at an unprecedented open hearing of the parliamentary Intelligence and Security Committee to answer questions about the work of their organisations.

Committee chairman and former foreign secretary Malcolm Rifkind said the open hearing marked "a very significant step forward in the transparency of our intelligence agencies".

It was televised with a two-minute time delay to prevent the inadvertent release of sensitive secrets.

But Mr Rifkind stressed that the MPs and peers on the panel, which normally grills the spy chiefs behind closed doors, would not ask anything that might lead to the revelation of secret information in public.

The Westminster hearing came amid intense debate over the role of the agencies following the disclosures by former US intelligence operative Edward Snowden of the surveillance activities of GCHQ and its US counterpart, the National Security Agency (NSA).

But Mr Parker rejected the idea that the scope of intelligence activities represented a threat to freedom.

He told the committee: "The suggestion that somehow what we do is somehow compromising freedom and democracy, of course we believe the opposite to be the case.

"The work we do is addressing directly threats to this country, to our way of life, to this country and to people who live in it.

"The work we do is proportionate judged against the necessity of protecting against these threats."

The agencies' budgets totalled around 6% of the UK's defence budget, said Mr Parker, adding: "We would contend that is a proportionate investment against the threats the country faces."

Mr Sawers told the committee: "It's not like it was in the Cold War. There aren't states out there trying to destroy our Government and our way of life. But there are a very wide range of diverse threats that we face.

"The biggest is terrorism - the threat from al-Qaeda and its many, many branches. There are also states out there that are trying to do us harm, through cyber-attacks, by acquiring nuclear weapons or involved in generating instability in parts of the world important to us.

"It's a very volatile and rapidly changing world we are living in and we have to have the skills, the people and the capabilities to be able to support and defend this country's security interests wherever those threats arise."