Scene: the garden of the Flower Pot inn at Aston, a hamlet two miles from Henley-on-Thames. Time: 7.45 on Tuesday morning. Brilliant early sun is slanting through old apple trees and washing over the wooded Chiltern hills in the distance. Enter 75 bikers, almost all wearing white T-shirts emblazoned fore and aft with the legends "Inverness to Dover - National Cycle Network" and "Sustrans - Paths for People".

This was Day 25 of the 1,000-mile ride organised by Sustrans (short for "Sustainable Transport"), and designed to raise awareness of the Bristol charity's campaign for a nationwide system of cycle paths. You could pick out the 20-odd hard-core riders, who had come all the way, by their nut- brown faces, arms and knees: the rest, like myself, were joining for shorter stretches.

We were briefed by Jeremy Iles, our leader, a tough-looking fellow who warned us that he did not want any repetition of an incident the previous day, when a girl had been clipped by a van, lost her temper and kicked the offending vehicle. "This isn't a demonstration of bikes versus cars," he said. "Our job is to promote a positive image of cycling."

Then we were off in a straggling crocodile, along a route negotiated in advance: private farm roads, cart-tracks, bridleways and footpaths took us past the glorious red-brick Georgian facade of Culham Court, past Hurley, past haunted Bisham Abbey and into Stanley Spencer country at Cookham.

Everything was fluid and easy: the riders streamed into small groups, broke up, reformed, all in sunny mood, all ready to talk. Most had joined the ride to do something for the environment. Several reckoned the expedition would cost them more than pounds 1,000, even though they were camping or staying in youth hostels.

John Treleaven - at 76 the oldest on parade - cheerfully observed that he could have had a holiday in Australia for the same price. A diminutive former civil servant, he insisted that it was only his fellow-riders who had kept him going: "They've almost towed me along."

Our first stop was at Cliveden, the great house poised above the Thames at Taplow, once the home of the Astors, now owned by the National Trust, who entertained the travelling horde with coffee, tea and flapjacks. A trust representative spoke warmly of the role bikes can play in reducing the use of cars, and the actress Jenny Agutter echoed him with a few graceful words.

Refreshed, we sped across Dorney Common to join the Thames towpath and follow the river to Eton and Windsor. After sandwiches and drinks at the Castle Hotel - by courtesy of Trust House Forte - the column wound on through Windsor Great Park to Runnymede, Staines, Laleham Abbey and eventually to Richmond. Reception followed reception, mostly given by local councils, and welcomed by Sustrans as evidence of the authorities' support for cycling initiatives.

The undoubted star of the show was Sheila Cameron, a stylish blonde from Dumfries. Until recently she was driving 35,000 miles a year as area controller for a retail company, "creating quite a traffic problem" on her own.

Having quit in disgust, she drummed up pounds 2,500 in sponsorship for a local Leonard Cheshire home, and set out on the great ride from Inverness on 10 June. But as she approached Durham 12 days later, she had a difference of opinion with a JCB, which left her with one forearm broken and the other elbow chipped.

A doctor forbade her to ride any further. She insisted she must. After a breathless hunt, Sustrans discovered an amazing machine: a Victorian Tandem, or tricycle made for two, on which a less-than-fit rider can sit in front, helping to pedal but not steering, guided by a fully-fit colleague behind.

The specialist maker in Redditch, Peter Taylor, whipped a brand-new model up to York and Sheila was able to continue, with one arm in plaster and the other in a sling. By her own account, she had to "become a tremendous flirt", soliciting a new male partner every day. Like John Treleaven, she paid warm tribute to the help her colleagues had given her. But in fact her courage has become the emblem of the ride.

On my short stage, I felt a sense of exhilaration and communal achievement pulsing through the column. Again and again I had the impression that I had come in on the crest of a wave, that recognition of the bicycle is suddenly building up, and that Sustrans's 16 years of campaigning are about to be rewarded by a breakthrough.

When the ride ends in Dover today, it will surely have increased by a substantial margin the chances of the cycle network project winning funds from the Millennium Commission.