The doubts began to set in about halfway up Farlington Avenue, on the outskirts of Portsmouth. The climb was described in my race notes as 'an early test of stamina'. I failed.

When I heard that the Tour de France was coming to Britain, I decided to cycle one of the two stages. The riders should arrive through the Channel Tunnel on 5 July, and race the next day from Dover to Brighton. I opted instead for the Hampshire stage, a 113-mile round trip from Portsmouth into the South Downs. The stage, on 7 July, is expected to take around four hours; I allowed myself three days.

My previous cycling experience had consisted largely of trips to the village to buy bread. On the few occasions when I had been out for a full day, the result had been a sore bum and a long lie-in the following morning, rather than a repeat performance.

Of greater concern were the gaps in my knowledge of bicycles. 'What shall I do if I get a puncture?' I asked the mechanic at Butler Cycles, as he talked me through the 10-speed gear system on the bike I had hired. He looked at me in disbelief.

'In this weather you're bound to get one,' he replied, 'so I'd better show you.' I left the shop with a borrowed spanner, a puncture repair kit and knowledge acquired from a 10- minute lesson on bike maintenance, which I knew I would forget.

Southsea Common on 7 July will be teeming with television crews, spectators, giant video screens, riders and gendarmes brought over from France to police the route. On a wet Wednesday morning in February, the sea was barely visible through the mist and the only signs of life were four workmen repairing the road and a woman walking her dog.

The aim was to travel as light as possible. But somehow the list of essentials grew longer each time I reviewed it: padlock, penknife, water bottle, first-aid kit, camera, alarm clock, notebook, chequebook, novel, cagoule, maps, spare T-shirts plus thermal underwear and warm clothes for the evenings - and, beneath my shorts, a money-belt strapped to my waist, containing not just cash but the details of my next of kin.

My plans to follow the exact route of the race were scuppered almost immediately by a policeman barring the entrance to HM Naval Base; he failed to see why the Independent should take precedence over national security. But soon I was leaving Portsmouth behind, with the sea breeze on my back and an exhilarating sense of freedom - until I reached Farlington Avenue. Five miles on the clock, 108 to go, and I faced the humiliation of getting off my bike and walking.

That was a turning point. Once I had accepted that this was not a virility test, that dismounting and pushing uphill was actually quicker than struggling in low gear, the whole task became easier. Adopting the Ranulph Fiennes approach ('Only 100 miles to the Pole'), I counted myself through manageable sections - 10 miles to Bishop's Waltham, 11 to Winchester, 14 to Andover - each rewarded with a drink or a snack. I reached Winchester for lunch, followed by three bars of chocolate and a walk round the cathedral.

Back on my bike, my spirits fell and rose with the hills. 'Have you come far?' asked the landlady of the guesthouse at Andover (42 miles), as I wheeled my bike into her garage. 'Portsmouth,' I replied as casually as possible, noting her astonished response with satisfaction. But her husband was less impressed. 'I used to cycle 20 miles to school and back,' he began, reminding me of Monty Python's Yorkshiremen sketch. 'Mind you, there was no traffic on the road in those days.' Taking my cue, I explained the purpose of my trip, but the couple were disappointingly unmoved. I had expected hoteliers to be anticipating the Tour more keenly than most, but on both nights my hosts - in contrast to the other people I met - seemed almost oblivious of the fact that it was coming at all (in contrast to the other people I met).

The next morning, pumping up the tyres, I heard a loud swish and the rear tyre went completely flat. The valve had come off with the cap, and the air would not return, however hard I tried. Salvation came in the form of a heroic mechanic at Halfords.

'You're doing this on your own?' he asked, surprised. 'Talk about making it hard for yourself. The competitors ride in groups, taking turns to protect each other from the wind. And they do it without luggage. And on better bikes.'

I cycled 45 miles that day. First to Basingstoke, two hours up and down, seemingly more up than down. At Basingstoke, a one-way system (which the Tour riders will be able to ignore) forced me to go the extra mile - but with a smile on my face, as I recalled the correspondence in the Independent in which one letter referred to Basingstoke as a prep-school euphemism for 'your flies are undone'.

I stopped for tea and treacle tart in Alton, opposite Jane Austen's house in Chawton village, and spent the night in Petersfield.

The following morning I spent time admiring Judy and John Sparrow's collection of teddy bears, some dating back to 1912. I could afford to relax. Previously, a 26-mile ride would have sounded an ordeal; now, it seemed like a rest day. I crossed into West Sussex and climbed South Harting Hill on foot. From here it was downhill almost all the way, which was just as well in bitter cold and heavy rain.

I sped into Portsmouth feeling relief, cold, pride, a sense of a challenge taken on and achieved. I reached Southsea Common at 4pm on Friday. When I crossed the line there was nobody to witness my feat. It had taken two days, six hours and 40 minutes. Not a world record, but definitely a personal best.

Tour de France: 6 July, Dover to Brighton via Folkestone, Canterbury, Ashford and Tunbridge Wells (128 miles); 7 July, Hampshire loop from Portsmouth, as described. Roads will be closed for at least 2 1/2 hours beforehand: check local details before setting out.

Jane Austen's House, Chawton, Alton, Hampshire. Open 11am- 4.30pm, April-October; weekends only, Nov-Mar.

Bear Museum, Dragon Street, Petersfield (0730 265108). Open 10am-5pm, Mon-Sat. Free.

Further information and accommodation lists from Tourist Information Centres at Portsmouth (0705 826722), Winchester (0962 840500), Andover (0264 324320), Basingstoke (0256 817618), Alton (0420 88448) and Petersfield (0730 268829).

(Photograph omitted)