For a Foreign Office man, the Honourable David Gore-Booth, Her Majesty's Ambassador to the Kingdom of Saudi Arabia, is engagingly frank. Does he believe Britain should be trading with unpleasant and oppressive Middle Eastern regimes? 'It is impossible for Britain to automatically exclude trade with anybody who can afford to buy British,' he says. 'You have to factor in the morality, but it cannot be the overriding factor because Britain has to survive by exporting.' So two fingers to the Scott inquiry, where the ambassador feels he was treated less than tenderly.

For a Foreign Office minister, even one aware of his own impending departure, the Rt Hon Tristan Garel-Jones is gloriously indiscreet. The unwitting distribution to the press of a confidential paper is 'a ghastly cock-up'. He has a gruesome meeting with the Italian Foreign Minister, the devout, cerebral Emilio Colombo. Afterwards a weary official concludes that Colombo was 'on another planet'. Garel-Jones agrees. 'That was about as near to hell as you can get . . . real zimmer frame stuff.'

About two years ago, the Permanent Under-Secretary, Sir David Gillmore, took a decision as uncharacteristic as it was risky. He agreed to permit the BBC to make a series of documentaries inside the Foreign Office. The team would be allowed to observe the most intimate moments of its rituals. The results, including Messrs Gore-Booth and Garel-Jones (who resigned in 1993) at their most acerbic, go on the air next week.

'We agreed with the Foreign Office that they could view the films to check for any serious breaches of national security,' said Stephen Lambert, producer of the series, 'and in fact they've only asked us to make two small changes which have not affected the editorial integrity of the films.'

The film-makers claim that 'never before has British television come so close to the heart of government'. The camera eavesdrops on private discussions between Douglas Hurd and his senior officials, follows the Bangkok consul into prison to meet British girls convicted of drug-smuggling, and captures an extraordinary secret lunch between a group of uncomfortable Danish diplomats and the British, meeting to plot their strategy to approve the Maastricht treaty.

Of course, as a Foreign Office telegram might put it, one should not necessarily conclude that this represents a conversion to the virtues of open government. There is, for example, no mention of the intelligence services or their agents in embassies abroad. Most of the brilliant intrigue and manipulation caught on film occurred almost two years ago, therefore a decent interval has elapsed to salve embarrassment and preserve reputations. No, this is a classic diplomatic gambit in which, by appearing to offer an enlightened concession, the Foreign Office is quietly promoting its own interests.

The aim is to defend the British diplomatic machine against the axe of the Treasury and to lobby at Westminster in a way it has never done before. Although the Foreign Office is envied and held in the highest esteem abroad, it is frequently derided at home. Ever since Munich, it has received a pretty dreadful press and is not exactly over-supplied with admirers in the House of Commons.

'The trouble with the Foreign Office,' says one Foreign Office minister (who shall be nameless), 'is that it contains too many people with soft hands.' Andrew Roberts, the iconoclastic historian, has even suggested that it could be dispensed with altogether in favour of a couple of fax machines.

For now, under the eye of the cameras, the British diplomatic service purrs on like David Gore-Booth's Rolls-Royce, showing the flag in Saudi Arabia to the despair of the Foreign Office inspectors, for whom such indulgence is always suspect. Cautious taxpayers will be relieved to see the inspectors cracking down on unauthorised claims by our diplomats in Washington for bottled water. They may be less impressed to notice that the inquisitors fly club class to get there.

Those who view the Foreign Office as a clubby male realm formed by public school and Oxbridge may be surprised by the consulate in Bangkok, the busiest outside Western Europe. It is run by Jean Sharpe, who has also served in Nairobi, Brussels and Dubai. The present ambassador in Beirut is a woman. The BBC team followed the formidable and devoutly Catholic Glynne Evans, head of the United Nations department, into Sarajevo, and tracked Frances Guy, the Iraq desk officer, on a visit to meet the Kurds of northern Iraq. Joint postings for married couples are not unknown. But the fact is that women are still under-represented: Glynne Evans, a self-confessed workaholic who is unmarried, is one of just 15 women in the top four grades, compared to 410 men.

The truth - and one hesitates to use a word so foreign to diplomacy - is that the Foreign Office has a mixed record but that its record is better than many people think. Take Munich, for a start. Britain's pre-war ambassadors in Berlin, Paris and Rome were all of disastrous political instinct but the Foreign Office itself harboured some of the fiercest opponents of appeasement.

The Foreign Office is held to be snobbish, but all concur that the service's favourite Foreign Secretary of all time was Ernest Bevin. It is true that some of our representatives inhabit agreeable homes by lakeside, palace moat or ancient city wall. But service in such pleasant surroundings is usually purchased by penance elsewhere. Which foreign correspondent or travelling businessman can forget the first diplomatic gin and tonic in a wintry Tehran, the dignified cupboard that served as Her Majesty's embassy in Croatia, or the urbane relief that greets the arrival of a fourth for bridge in Ulan Bator? The costs of running the entire diplomatic service in Whitehall with embassies and consulates abroad is about pounds 800m. The Social Security budget is more than pounds 60bn.

Rather like health insurance, it is hard to rationalise the cost of diplomacy until disaster strikes. Long before the advent of Margaret Thatcher, it was confidently proclaimed that embassies should devote themselves to exports promotion and ambassadors should become salesmen par excellence. Obedient and well-trained, the diplomats went efficiently to their task. It was, to say the least, unfortunate that the zenith of this policy was represented by Sir Anthony Parsons' embassy in Tehran, which proved so diligent in selling goods that it scarcely had time to observe that the Shah of Iran was about to be overthrown.

Foolish policy makes bad diplomacy, as it did in Iran before 1979 and in Iraq until 1990. The arms-to-Iraq folly has, perhaps, unsettled the most self-confident assumptions. Here is Gore-Booth again on film, arguing with British businessmen who want to sell to Iran and feel too much fuss is being made over Salman Rushdie. 'It's not just Rushdie,' counters Gore-Booth. 'We believe the Iranians are trying to acquire a nuclear bomb.' From the mouth of the man who was then head of the Middle East department, that is something of a scoop.

Garel-Jones tells the film-makers that the Government must decide whether Britain can retain its traditional high profile, with its seat on the UN Security Council, membership of the Group of Seven leading industrial nations, a leading role in the Commonwealth and a key, if unhappy, role in the European Union. He concludes: 'If you want to go on sitting at the top table, it carries a price.'

(Photographs omitted)