It is the story of my lunchtime drive from John Gummer's Department of the Environment in Marsham Street to the Grosvenor House Hotel in Park Lane. Or as the minister for London puts it more stirringly in his confidential letter, 'Moving from SW1 to W1.'
Across difficult terrain (Hyde Park Corner has to be negotiated) and with life- threatening distractions (one has to crane one's neck out of the car window at Buckingham Palace to see if the flag is flying and the Queen is at home) this was always going to be a dangerous journey. But armed with my Honda Concerto, and a copy of the Official Secrets Act I took a deep breath, put on some music and prepared to go over the top.
I knew it was going to be tough, this border crossing of postal codes, and I had to venture it three times to test Mr Gummer's theory. I set out from the Ministry in Marsham Street and headed for the Grosvenor House Hotel, a popular W1 haunt for ministers as it is the venue for numerous dinners and receptions. First I took the government-recommended crossing. From Marsham Street through Parliament Square (not even attempting the back doubles via Queen Anne's Gate as they were sure to be classified). I moved sweetly through Horse Guards Road, where incidentally I passed only two private cars - a road waiting to be pedestrian ised surely - then along the Mall, past the palace and up Park Lane. The two and half miles took exactly 11 minutes.
I then took the obvious alternative route, substituting Birdcage Walk for Horse Guards Road and the Mall. Mr Gummer was half right. There was a time difference. He just happened to be completely wrong. The distance was actually shorter by half a mile and the time shorter by two minutes. Our country's leaders are actually wasting taxpayers' money by telling their drivers to cut through Horse Guards Road. It's longer. But to be fair to Mr Gummer, I tried one other route, through Whitehall and turning left into Trafalgar Square then up the Mall.
This was indeed longer by half a mile, and longer in time by four minutes. Sitting in a very small queue of traffic, the only one I encountered, I did, I regret, throw my chewing gum out of the window, which is perhaps what the Chancellor of the Exchequer had in mind when he wrote in his letter that if Horse Guards Road were closed, 'the environmental impact of this on Whitehall should not be under-estimated'.
Nevertheless, for a Minister for London, there are advantages of being stuck for 50 seconds in a queue at the corner of Whitehall. He would have noticed that the Whitehall Theatre was dark and no doubt would have increased funding to the arts in London. He would have noticed the lack of pavement cafes in Whitehall, he may even have noticed the number of civil servants in cars who could have been walking.
So, Mr Gummer should take heart. His crossing from SW1 to W1 will be quicker if going through Birdcage Walk; and if he insists on choosing Whitehall, well, there are tourists, summer fashions and guards marching up and down. Enjoy the scenery. In confidence.