Monica Hills, 63, is leading the walk. She marches ahead, knobbly stick in hand, shouting orders to the convoy. "This way, this way!" she bustles, as 60 of us slow up to get through a turnstile that leads to the river. We then make a crocodile formation and walk along a towpath, admiring the expanse of green fields and woodland ahead.
I catch up with a woman dressed smartly in a white polo neck and pearls. Louise Hill, a parish councillor in her fifties, feels strongly about preserving footpaths. "I'm constantly bothered by farmers. Why should these landowners have one set of rules for themselves?"
But when it comes to prot-esting, Mrs Hill is no Bright-lingsea radical. "Demonstrators could put back the good work that we do. Some of these people aren't very diplomatic, are they?" She frowns. "If I started bawling and throwing things, it wouldn't change a thing. One has to go about it gently and persuasively."
Today, there are more pressing concerns. We all stopto look at some local paintings exhibited at a small lock.
But Mrs Hill and friends may soon be in for a shock, for the Ramblers' Association - bastion of class harmony and polite negotiation - is a-changing.
Last April, the famously yoof-ful Janet Street-Porter was elected president. Earlier this month, Kate Ashbrook, a campaigner for ramblers' rights, became chairwoman - at 40, the youngest person to hold the post - having been elected on a platform of change. Her speech at the annual general meeting was impassioned and vociferous: "We will lead a new crackdown on those landowners who persistently and illegally block footpaths," she cried. "Either reform your ways now, or change will be imposed on you."
These are stirring words for an association whose hardcore members are typically 55 years old and above. But part of her brief is to modernise the Ramblers' antiquated image.
"I want people to associate us with something absolutely up-to-date," she explains briskly.
"We're encouraging people to be more confrontational and stand up for their rights. We've tried to negotiate gently, but you can't do that forever."
At the annual general meeting, a motion was passed calling on the Queen, no less, to allow a public right of way by the Thames at Windsor Castle.
The new approach seems to be working: the average age of members has dropped to the late forties, with many younger people joining local groups.According to the Ramblers' Association spokeswoman, Sue Bond, out of 104,000 members, 50 per cent join to enjoy the companionship of walking, but the rest are more interested in the campaigning side.
Last October, they marked their 60th birthday with a campaign aimed at recalcitrant landowners. This will include targeting 60 blocked footpaths in Bedfordshire, as well as "right to roam" demonstrations in the Pennines.
One of the new breed is 21-year-old Kevin Matthews, publicity officer for the Nottinghamshire area Ramblers and a business studies student at Trent University. "There have been many cases in the past where we've tried to negotiate and got absolutely nowhere," he says. "We're in the position now where we can do nothing else but encourage public support for demonstrations - peaceful ones, of course. I think we have to stand up for our rights."
Mr Matthews recently add-ressed the environmental wing of his student union on how the Criminal Justice Bill can affect walkers' access to land. But the new image still has some way to go. "At university, a lot of people still think of us as just a national walking club. They don't realise that we're younger and more radical these days."
Many older members, particularly in the north of England, share Mr Matthews's enthusiasm. "The last few years have seen a real shift in emphasis," says Alan Hutchinson, 46, who joined 13 years ago after a farmer tried to drive him off a public bridleway. He is secretary for the Ramblers' Darlington group and chairman of the North Yorkshire and South Durham area. At the moment, they are campaigning for public access to Mickle Fell, the highest point in County Durham.
"Ramblers are out fighting for the rights of all walkers," says Mr Hutchinson. "I see that as our primary role."
As Kate Ashbrook points out, "I made it clear what I stood for at the annual general meeting. I want us to be an effective campaigning body. All I'm saying is, why should walkers be treated as second-class citizens?"
Back in Berkshire, however, the word "campaigning" still carries vulgar connotations. "It's a sad state of affairs," says Louise Hill, "when these rent-a-crowd demonstrators turn up and start getting a bit rough."
Another lady in a silk scarf and Barbour strides ahead. Does she feel strongly about the campaigning side of the Ramblers' Association? "Yes, but I don't think I'd actually like to take part myself," says 52-year- old Yvonne Wright, a visitor from Bristol. "We have very few problems in our area, so it's not something that really concerns me."
Does she think a younger president and chairwoman is a step forward for the association? "You mean Janet Street-Porter? She's hardly the country type. I can't imagine her even being interested in outdoor pursuits," says Mrs Wright.
Her husband, Geoff, 59, joins in. "That sort seem so interested in issues and causes. The main interest is walking and we shouldn't get away from that."
A young man stands on his own, wearing Dr Martens and a green army jacket. He is the only one here who is at least suitably dressed for some direct action.But 32-year-old Toby appears to have come along under pressure from his parents. "Like a number of other people I'm just apathetic about it, really."
Meanwhile, Louise Hill'sattention wanders. She points at the ground excitedly, while her neighbour coos in appreciation. "Oh, look!" she exclaims. "A variegated clover!"