Day of the post ­Christmas river trip, so no long lie­-in. Rewarded by quiet streets and have time to show Granny our new office location in Tavistock Street and Waterloo and Blackfriars Bridge views before gathering with the others for the 10.30 boat from Embankment Pier to Greenwich. Full family turnout. Eleven in all. Onto a barge with chairs and a plastic hood. It’s a quarter full, almost entirely of foreigners, as we turn under Charing Cross railway bridge and head downstream.

A Cockney commentary, full of jokes of the corniest sort and not even told with any charm, just routine taxi­-driver sort of prejudices. Edward and especially Catherine Burd, both architects, made apoplectic by references to the National Theatre – ‘thought by most architects to be the worst building in London’. Piers Gough’s Cascade Towers – ‘they say they were designed to look like a boat under full sail. Well all I can say is he’s obviously never been on a boat in his life’, and the Millennium Dome – ‘biggest waste of taxpayers’ money this country’s ever seen’.

In a way I prefer this batty bigotry to a recorded message, but that’s quite a perverse view to take.

An hour to Greenwich and the changes along both banks are considerable. Housing runs in a broken line on the south bank and an almost continuous line on the north, all the way to Greenwich. Canary Wharf is expanding again, after its dodgy hiatus in the late ’80s and the bombing in the ’90s. London’s eastward spread looks inevitable and unstoppable now.

The Dome, a strange new shape, a blister amongst the strips of housing and the fingers of the tower blocks, looms beyond Greenwich’s elegant seven­teenth­ and eighteenth­ century façades.

We climb up the hill to the Observatory, following an ant­-trail of visitors. There is a space on the wall below Flamsteed’s Wren­ designed building where the zero line of longitude runs. It’s covered in graffiti.

Last day of my out of London signings. A week in which I estimate, conservatively, that I’ve signed five and a half thousand books, and in which we hit the No. 1 slot on the Sunday Times list in some style, with figures of 31,700, 11,000 more than Bryson in second place and considerably more than even the big Christmas paperbacks – Pratchett and Francis and Bridget Jones’s Diary.

Lunch at the invitation of Karen Wright of Modern Painters. She has commissioned a cover from Tracey Emin. ‘The first cover we’ve ever commissioned,’ she says proudly. Unfortunately Tracey’s contribution is an embroidered square reading ‘Fuck Modern Painting’. Karen is distraught. Her husband says he’ll leave her if she puts it on the cover. W. H. Smith will refuse to stock it. I really can’t understand her pusillanimity. If you commission from Tracey Emin, this is what you get. Anyway, it’s rather colourful and sweet and quite a good joke.

My morning is cheered by a report in the Guardian of a man who fell a hun­dred feet down a hillside trying to avoid a ‘bouncing 8lb Double Gloucester cheese’. Actually, his injuries sound quite severe, so I shouldn’t really have smiled so much.

Receive a fax from Tom Dunne – handwritten, which is his style – to say that he has read Hemingway’s Chair. ‘Good clean fun’ is his three word assessment. He would like to publish it in the US next spring.

Up for a run at eight. In West Meadow a harmless­ looking beige Labrador lollops towards me and delivers a sharp nip to the back of my left leg. I’m not moving fast, there’s no question of shock or surprise, or even aggression on the dog’s part; he just came over and bit me. His owner is a lean, quite elderly man I frequently see. He doesn’t seem much put out. ‘I’ll give him a good hiding,’ he says, with a grin.

Run on. Lloyd Dorfman is walking up Lime Avenue. He’s most concerned by the news, says I should go to hospital and have a tetanus jab. Run on for quite a way in nervous apprehension of my body suddenly freezing in mid­-motion, before I remember that I’m covered for tetanus until 1998.

Into the West End to have my photograph taken with Helen’s surgeon, Michael Powell, at the National Hospital. Both of us, at his request, to be dressed as per his favourite Python sketch – the Gumby brain surgeons.

He’s brought along what Gumby kit he can muster, in a carrier bag. So find myself in a most surreal situation; dressed in gumboots, knotted handkerchief and brandishing a surgical steel bradawl above the head of one of Britain’s leading brain surgeons.

After it’s done we remove our gumboots and hankies and he offers to show me the theatre in which H had her op. We go through into a small, narrow room, when he breaks off – ‘Oh dear, there’s someone in here.’ We both peer round the door and there is indeed someone in there, shrouded in hospital green, laid at a 45° angle with a surgeon working in their spotlit head. Powell is quite unfazed; exchanges some boisterous greetings, which are returned from one of the masked figures around the body.

Papers full of the potentially appalling consequences of the BSE, mad cow affair, after scientists have gone public with their strong suspicion that BSE has leapt a species and infected humans who have eaten beef. No hard facts or advice. Everyone frightened.

As H says, the CJD disease takes ten years to incubate, and so our children, who ate beef in the late ’80s, could, like us, be very much at risk if there is an epidemic. Apocalyptic news which vies with details of a huge increase in airborne tuberculosis, which is already on its way to becoming a new, life­threatening epidemic. There’ll be some reading of the Book of Revelation tonight.

The rain which began as persistent drizzle this morning is now coming down in a series of increasingly heavy downpours. The silhouetted figures, hunched beneath capes, riding bicycles and scooters and pedalling cyclos, look like the stragglers of some retreating army.

The room is fairly shabby and small and has no bath or river view, but the bed’s comfortable and I rather like its cell-­like intimacy.

Vietnam is the most demanding country we’ve yet filmed. Though there are signs of accelerating modernisation and change it is still a modestly equipped Third World economy.

Beggars wait at all tourist pick­up points, extending bony, withered hands, or shuffling legless torsos towards the steps of the bus. Wherever we go where tourists are seen, there is a nudging at the elbow and an imploring look. Chil­dren, often beautiful and irresistibly bright-­eyed, hold out their open palms, or demand pens or chewing gum. Along most of the inner­-city streets there are open drains, and in Hanoi many ponds and canals clogged thick with rubbish and human waste.

One of the advantages of the raw, unpolished, Third World feel of Vietnam is that almost everything you point the camera at is interesting – and Roger has found a good number of English­-speaking Vietnamese to be my companions.

This is good, purposeful travelling. Rough and ready, unpredictable, demanding but full of character and incident.