The intelligence officer

In 1991, with the ice of the Cold War still melting, the then head of MI6, Colin McColl, made a prediction that looks startlingly accurate today. "You can be assured that despite all the changes that are happening in the world today – the crumbling of the Iron Curtain, the increasing closeness of Britain to our European partners, the problems in the Middle East – MI6 has a bright, certain and exciting future."

Emphasising close Anglo-American intelligence links dating back to the Second World War, he added: "Our greatest allies will continue to be our American cousins. The relationship between MI6 and the CIA is central to the special relationship between our countries."

Mr McColl – or "C", as the head of MI6 has always been known – was welcoming a group of new recruits to one of the world's most famous spy agencies. Despite Mr McColl's confidence, for a while after the Cold War the future of Britain's intelligence services looked rather uncertain. Some critics even suggested that, with no communist bloc to spy on, they should be dismantled.

But with the IRA bombings of the mid-1990s, diversification into drugs and organised crime intelligence, watching for nuclear and biological warfare proliferation, British intelligence officers still had their uses.

If anything, the importance of MI6 has grown. In 1994 MI6 moved into a new Terry Farrell-designed building on the banks of the Thames by Vauxhall Bridge, costing some £250m – which is jokingly referred to by staff as "Ceauscescu Towers", after the late Romanian dictator and his taste for bombastic architecture. In the world of cloak and dagger, MI6 is in charge of Britain's foreign intelligence-gathering. It works closely with its colleagues on the other side of the Thames, MI5, whose job is to gather intelligence within Britain. MI5 monitors the movements of anyone suspected of having terrorist connections, while Government Communication Headquarters (GCHQ) taps telephones, mobile phones, emails and faxes from its base in Cheltenham.

Ten years on, several of the raw recruits who heard Mr McColl's prophetic words are now senior officers working as part of the team that is tasked with spying on Mr bin Laden and his al-Qa'ida network. Their job is to disrupt the network's operations. And by all accounts they are doing a good job. Since 11 September, Britain's intelligence services have gone on to on a war footing. Holidays have been cancelled, and many officers are sleeping in their secret overnight bases. They rush around with the latest telephone-tap transcript or write the ultra-secret reports that are given to senior members of the Government.

Most days, senior officers from the three intelligence services meet at the Joint Intelligence Committee in the Cabinet Office in Whitehall to discuss any new intelligence on Osama bin Laden. Much is shared with their American counterparts. Every few days, MI6 chief Richard Dearlove and MI6 boss Stephen Lander visit 10 Downing Street to update the Prime Minister and the Home Secretary.

Deep in the heart of MI6's offices is a secure command-and-control room from where MI6 runs its major operations. It was here that Serbian war criminals were tracked and arrested by the SAS. Now it is filled with the earnest members of the Middle East task force. A surprisingly youthful group, they sort through agent reports and detailed analysis from officers stationed across the world.

Upstairs, meanwhile, one of MI6's financial analysis teams is working in the part of the building that still carries slight scars from a Real IRA rocket attack two years ago. The team's job is identify Mr bin Laden and his associates' financial network so that bank accounts can be frozen, depriving al-Qa'ida of money to carry out further operations.

"The impetus of the last few weeks has meant we have been able to identify more accounts we believe are connected to terrorists and with the political climate in our favour we can get them shut down. If only it was this easy normally," said one officer.

A British intelligence source told me that MI6 has made efforts to modernise. The agency was shaken by the bad publicity generated by a renegade officer, Richard Tomlinson. Although it has made no public admission – it never makes any public statements – it recognised that many of the criticisms made by Mr Tomlinson about poor management and recruitment were true.

When Mr Tomlinson joined in 1991 there was still a whiff of the old-boy network when it came to recruitment. There were nine recruits in his group, all men, most of them ex-public school, Oxbridge graduates or from top-notch regiments like the Scots Guards. Only 10 per cent of officers were female; none was from a black or Asian background.

"MI6 now tries to avoid the public schools and Oxbridge. It prefers to recruit from the red-brick universities," said one officer. "We are more interested these days in the computer nerd who can hack into financial record trails than derring-do public schoolboys."

One of the biggest problems in tackling Mr bin Laden has been getting spies into his camp. "High technology that taps phones and takes photos from space is all very well but there is no substitute for the spy in the enemy camp," the officer said. The days when a white-skinned Englishman could disguise himself by wrapping himself in a scarf and rubbing boot polish on his face to penetrate the Arab camp went out with T E Lawrence.

MI6 is well aware that the lack of black and Asian officers has retarded its ability to penetrate Islamic extremist groups and to win over informers within such organisations.

"During the Cold War, you would get insiders who would give you information for ideological or financial reasons. With the Islamic extremists groups, this just doesn't happen. We have to get our intelligence other ways. This is difficult."