What does it do?

Now that Spooks has established itself in prime-time television schedules many people will have an insight into the work of the organisation whose very existence was not officially acknowledged until relatively recently. More formally known as the Security Service, MI5 works to protect the country from threats to national security, chiefly terrorism, spying and serious crime. It does this by working behind the scenes to collect and assess intelligence, and then intercept the threat. Understandably, MI5's work has gained new prominence since the 11 September 2001 attacks in the USA, and the 7 July bombings in London. The organisation will celebrate its centenary in 2009.

Vital statistics:

There are 2,550 staff; the aim is to increase the workforce to more than 3,000 by 2008.

The office:

Most staff are based at Thames House, near Parliament. However, there are some employees in Northern Ireland, and new offices will soon be opening in regional locations around Britain.

Is this you?

Graduates are taken on as "desk officers," for which you'll need a 2:1 in any subject, plus a year's work experience. Non-graduates, with top drawer A-levels and four years' work experience are also considered. Other qualities required include decisiveness, integrity, discretion and an incisive intellect. You must be a British citizen with at least one British parent. Around 70 desk officers are recruited every year.

The recruitment process:

Applications via the website ( www.mi5.gov.uk) go through several sifting stages, culminating in a face to face interview with a member of the Security Service, a one-day assessment centre at Thames House, and a final selection board. Because of the vetting process, applicants must limit those they tell about their application to their partner and immediate family. All desk officers have a 14-month training programme, the first ten weeks of which cover core skills, particularly intelligence and analysis training. To find out how the actual job fits in to the broader picture of counter terrorism work, read the "day in the life" of a desk officer at www.mi5careers.info. For the first six months, recruits are mentored by an existing desk officer.

Top dollar?

The starting salary for desk officers is £22,000.

Beam me up Scotty?

Most desk officers aim to get their first promotion after 18 months. Many go on to a middle management position, leading a team of around ten, in around five to six years.

Who's the boss?

Dame Eliza Manningham-Buller (above) has been Director General since 2002. She joined in 1974 after three years as a school teacher.

Little known fact:

MI5 make a point of saying they do not exclude ex-drug-takers from joining, providing recruits are honest about their past, and undertake to steer clear of drugs, in any form, in the future.