Away we pedalled, like a multi-coloured snake wriggling through the streets

Who's got pole position?" cried the Mayor of Llanwrtyd Wells merrily from the steps of the Victoria Hall. His necklace of medallions flashed as he beamed down on us. "I hope we shall see you all again sometime. But now it's my pleasure to say 'GO!'"

Away we went. Not all at once, because that would have been impossible with 167 bikes in the confines of a small Welsh spa town, but in a steadily- elongating, multi-coloured snake, which wriggled off through the streets and out into the surrounding hills on a cool, grey morning.

So began Day 13 of the Belfast-to-Land's End trail-blazing ride organised by Sustrans, the Bristol-based charity which is creating the National Cycle Network. If last year's ride, from Inverness to Dover, was an immense success, this year's is proving a triumphal progress: more people are taking part, and support from local organisations along the route is immeasurably greater.

Thus, as we pedalled southwards, people spoke in awe of the terrific spread laid on the previous evening by the Llanwrtyd Wells Town Council. Such were the mountains of sandwiches and cakes that not even the army of ravenous bikers had been able to finish them.

People also spoke grimly of the weather they had been through. The opening ceremony, outside the City Hall in Belfast, took place in a torrential deluge, and the rain on the first days had been so fierce that it beat the oil out of chains and gear-wheels, with the result that several machines seized up.

For me, the greatest pleasure lay in the unfailing friendliness of my fellow-riders:although groups were constantly changing as people moved up and down the line, everybody was ready to talk.

The bikers could hardly have been more diverse in origin and nature. Chris Le Breton, an environmental officer with the European Commission, had come from Brussels, where he devises management programmes for the Black, Caspian and Aral Seas. One of the most resolute (but also most decorative) cyclists was Emily Shirley, riding a tandem with her two-and- a-half-year-old son Finbar perched on a little seat just behind the handlebars, her eight-year-old daughter Meg pounding on specially built-up pedals behind.

The machines were equally heterogeneous, from bone-shaker to state of the art. Malcolm Brenchley, a retired dental surgeon from Devon, and his wife Vera had spent pounds 2,500 on a new tandem. Cynthia Kirby, a great-grandmother from Norwich, was giving a first run to her custom-built Bike Friday, which had cost her pounds 1,500.

As we whirred down a minor road on the east bank of the Wye, I had breath for a chat with Phil Insall, a leading light of Sustrans. He described how the organisation, gavlanised by a grant of pounds 43.5 million from the Millennium Fund, had expanded furiously over the past year, and how the target of a national network is now definitely within reach. As originally proposed, the network was 5000 miles long. Now, because so many local authorities want to be included, it has been extended to 6,500 miles. The aim is that half should be on road, half on traffic-free paths also open to pedestrians. The cost will be about pounds 190 million. Nearly half should be finished by the year 2000, the rest by 2005.

In such a gathering, nobody much likes cars. The Pollution Solution proclaimed the backs of several T-shirts - and the only altercation I witnessed came when a white van shot over the brow of a hill so fast that it had to do an emergency stop. Although nobody was hit or hurt, the driver began abusing us for blocking the road - but within seconds he was surrounded by a swarm of bikers, who saw him off as smartly as if they had been bees.

At Hay the ride split. Half went on over the fearsome Gospel Pass and down to Abergavenny; the rest of us took a gentler route to Brecon, which we approached as evening sun gilded the ridges of the Beacons high on our left, and we came to rest at last with 52 miles behind us.

It was a tragedy for all concerned that Geoff Hamilton, presenter of BBC TV's Gardeners' World, should have died of a heart attack during this stage last Sunday. Millions will mourn him and his death inevitably cast a shadow over the ride. But Sustrans will pedal on; and when the cavalcade rolls into Penzance next weekend, the great goal of a complete national network will be that much closer.