TOURS / Getting lost in the post office: Dominic Cavendish finds sinister goings-on at the post office

The Japanese, the Germans, they all come here and look at it. . . but they can't have it. It's unique and they're all jealous.' Before the evening tour of London's Mount Pleasant sorting office is even underway, Pat Hickey-Hynes tries to impress upon visitors that they are about to survey one of the last vestiges of Britain's greatness.

Postal sorting offices may be two a penny, but the one that occupies the seven-and-a-half-acre site at Mount Pleasant is something of a collector's item. Not only can it boast being Europe's largest sorting office, but it is also one of a handful of stations on the world's only underground mail railway.

Tonight's tour had been group booked by a dozen Amnesty International workers from round the corner, all relishing the fact-laden atmosphere. They have an Irish guide called Pat. . . the evening promises to deliver.

In order not to appear mere train spotters, the group abstains from rushing to glimpse the Whitechapel to Paddington mail line and instead spends two-and-a-half hours in the vast sorting office.

Computers enable the 105-year-old office to process 17 million letters a week, including 80 per cent of incoming international mail. Humans tend to be overshadowed by the 24-hour-a-day mechanical sifting. As a consequence the visitor gets both a taste of Willy Wonka and a sense of Orwellian gloom. Rows of earphone-dependent operators punch in area codes at the rate of one a second. Signs warn that 'Every letter is important to someone' and the blank windows of security watchtowers are never far away. You are reminded of Auden's propaganda piece for the GPO, Night Mail, and its sinister twist ('None will hear the postman's knock / Without a quickening of the heart.')

But the machines have not taken over. A bit of human nous is required for some items to get through. For starters, machines can't read people's postcards yet. 'Most people's postcards are dead boring,' says Pat, 'just going on about the weather.' Sorters prefer deciphering cryptic addresses. A special squad of 'detectives' resides on the ground floor. In among the letters to Sir John Gielgud and cheeky crossword clue addresses lie the utterly surreal: 'No point writing your address as it's going to our house,' reads one. Steve Spratt, Manager of the Mechanised Coding Area, enjoys oddball bits of post. 'We phone London Zoo quite a lot to pick up the snakes and spiders.'

Compared to the commotion upstairs the computer-controlled diminutive Mail Rail seems rather a let-down, but Nick, a self-confessed underground junkie, is thrilled. 'I love the magic of deserted underground stations. They remind me of my childhood.'

'You get all this for just 25p,' says Pat, over the free tea and biscuits that round off the tour. 'I think the British postal system is the best in the world. It only works because it's a monopoly. If they ever privatised this they would be kicking all our extra little services out the window.' Including, perhaps, the free tour. Hurry, or you'll miss it.

To book a daily tour (max 30 people) write to The Security Manager, Royal Mail Mount Pleasant, Farringdon Rd, London, EC1A 1BB. Times vary.

(Photograph omitted)