The Cold War may be over, but as the case of the former MI6 spy Richard Tomlinson shows, there is still plenty of cut and thrust in the covert world of state intelligence.

Of course things have changed dramatically since the era of Burgess and McLean. Britain's two main security services, MI5 (domestic operations) and MI6 (overseas), like the CIA in America, have suffered budget cuts and problems with staff morale.

Spies may have given China the ability to detect UK Trident nuclear submarines

The new openness has exposed them to greater scrutiny and, inevitably, criticism. The cases of Tomlinson and that of ex-MI5 spook David Shayler are cases in point.

And recruitment is no longer down to the simple "old school tie" principle, but instead conducted through newspaper advertisements and telephone inquiry lines.

Added to this is the fact that it is now more difficult than ever to "know your enemy". The days of the monolithic enemy - Soviet communism - are long gone.

But something that has not altered, at least according to the chairman of the Parliamentary Intelligence and Security Committee, Tom King MP, is the work level.

Earlier this year, Mr King sought to justify the role of security services in this post-Berlin Wall age, and the �700m annual funding they receive.

"This is a more complicated world. The threats are changing. They are no less but are not the same nature," he said.

David Shayler - a former MI5 spy

Paul Wilkinson, a professor in International Relations at St Andrews University, agrees.

"The business of spying is still very active. It's still a very important aspect of the security of every large and most middle-sized powers, as well as smaller countries that are in a threatening situation."

One of the most high-profile targets of intelligence services is terrorism.

Despite the peace process in Northern Ireland, terrorism is still viewed as a major threat in the UK's corridors of power. Stella Rimington, before she finished as head of MI5, said it took up about 50% of the agency's time.

The bombings of US embassies in Nairobi and Dar es Salaam last August, raised the stakes in the war against international terrorism.

Blame for the attacks was pinned on the Islamic fundamentalist Osama bin Laden and America's subsequent missile strikes on targets in Sudan and Afghanistan were, it is claimed, the result of its international intelligence operations.

Spying in the air - a U2 spy plane

British agents in this field operate both in the UK and abroad, where their mission is to protect British assets.

Organised crime, traditionally targeted by regular police, was added to the remit of the UK's security services in 1995/6. It encompasses the fight against drug trafficking, arms shipments and money-laundering.

The decision to add it to the portfolios of MI5 and MI6, or "five" and "six" as they are known in the trade, led to concerns they were becoming overloaded with work.

Involvement in espionage and counter-espionage is largely a "continuation of the traditional role, in so far as we still have states against us," says Prof Wilkinson.

On the surface, relations between the UK and Russia may be better than at anytime during the Cold War, but scratch deeper and there is still great uncertainty.

"While Russia may be a friendly face at the moment, there are uncertainties about it in the long-term. Will groups that are very anti-Western in the Russian Duma push the present, moderate leadership and form a leadership that is much more hostile?"

Iraqi leader Saddam Hussein - a target of US counter-proliferation work

A recent document from the United States National Counter Intelligence Centre revealed total espionage activities in the US have increased. "Some are traditional adversaries while others are long-term allies of the US," the report said.

Industrial and economic espionage has witnessed huge growth as technology has become more powerful and accessible. It is the job of security operatives to keep track of equipment which might fall into the "wrong hands".

Another aspect is that seemingly benign technologies may have a dual use and so be used for military purposes.

This spills over into the fight by Western governments to stop the spread of nuclear and chemical weapons - counter-proliferation.

"We live in an age where a number of regimes are trying to equip themselves with nuclear or chemical weapons - weapons of mass destruction," said Prof Wilkinson.

Plans depicting India's nuclear test site which took the CIA by surprise

"The proliferation of missile technology allows countries with just modest means, modest wealth, to launch their own missile programme. Given the availability of satellite GPS (Global Positioning System) it's fairly easily done."

Keeping track is somewhat harder, as can be seen in the case of India's first nuclear test, last year, which caught the rest of the world completely by surprise.

Yet Prof Wilkinson says that while intelligence services often take the rap, mistake may be the fault of governments which chose not to act of information.

And he remains convinced of the need for secret intelligence.