She's a persuasive woman Alison Cobb. With an old map of Oxford covering her kitchen table, it took her all of three-and-a-half minutes to convince me that we were looking upon the answer to Oxford's flooding problems.

Her finger ran across the map dating from 1919 before she suddenly declared: "That's it. Can you see the word 'overflow'?"

She had invited me to study the old map at her Binsey home to support her long-held argument that rather than looking at spending more than£100m on creating a flood relief channel or vast water storage areas, the Environment Agency should be considering a far simpler solution right under its nose.

It all comes down to the lost Swift Ditch, a watercourse that once ran from Port Meadow, near Godstow Lock, to the Seacourt Stream.

For 300 years it served the useful purpose of carrying Thames floodwater away from the village where she has lived for 20 years.

But it has disappeared - with, Mrs Cobb argues, devastating consequences for residents.

And remarkably, its disappearance could now be the subject of the first legal action against the Environment Agency in the wake of this summer's floods.

The night before we met, Mrs Cobb had urged 100 flood victims at a public meeting to pull together to mount a joint legal challenge.

She proposed they seek legal advice for a 'class action' against the agency, an American term for legal proceedings involving a group of people whose case involves a common question in law.

It was certainly a bold course to follow, given that group legal actions are almost unheard of in relation to flood incidents.

It was all the more remarkable that the legal challenge she is calling for centres on a ditch that had acted as an overflow from Port Meadow since 1792.

Yet the Binsey Residents' Association chairman appears more than ready to take on the might of a multi-million-pound agency, with its legions of engineers and flood defence specialists, on a purely technical matter involving water flow.

She set out her case in detail at a packed meeting at the West Oxford Community Centre, in Botley Road, where residents once again vented their fury on an Environment Agency representative for having allegedly left them again without adequate flood defences.

In something of a coup de théâtre she had brandished the old map at the meeting, before delivering a detailed argument for some serious ditch clearing.

With only the promise of ongoing investigations and consultation to offer residents, the EA man, Rob Alexander, had dismissed Mrs Cobb's case.

"It's not that simple," Mr Alexander, the asset system management team leader of the EA's Flood Risk Management Department, protested.

But, by then, many had been easily won over by the persuasive village flood warden.

Her call that there is too much PR around and not enough blokes with shovels had certainly struck a chord with West Oxford residents.

Besides that, many people know that she has made a close study of the streams, ditches and waterways around the tiny hamlet on the edge of Oxford over years.

"The agency is to blame. I suggest that we do a class action and take them to court and make them pay for everybody that was flooded." she said. "They knew what to do, and they did not do it."

Others quickly offered their support.

John Power, the former Lord Mayor of Oxford and general secretary of the Osney, St Thomas and New Botley Allotment Association, said: "I agree with her totally. I am certainly prepared to make my contribution towards it.

"They are a completely inactive, useless organisation - a flood defence organisation that does not defend us against floods."

So, with so much resting on it, the invitation to join Mrs Cobb in search of the missing Swift Ditch was irresistible.

I could see from the map that it hardly amounted to the search for the source of the Nile.

But I could not help wondering how the EA, its predecessors and local landowners managed to let it go missing?

Were Mrs Cobb and her husband, Stephen, who runs his own environmental consultancy company, just a couple of obsessives, driven to understandable distraction by the constant threat of flooding?

Or could Swift Ditch and the Seacourt Stream really hold out the prospect of salvation?

We were to be joined on our search by a retired teacher, Colin Hanniford, of Duke Street, who arrived as we were just setting off.

Mr Hanniford had managed to escape serious flood damage but he had, nevertheless, been inspired by her speech to cycle over to her home to support her campaign in any way he could.

Driving past The Perch pub, still being renovated after a devastating fire, we headed towards St Margaret's church, past fields which just weeks ago resembled Lake Ontario.

"Because Swift Ditch is not working, the water goes to Binsey, and then from Binsey to Botley," she explained as we bumped along an increasingly narrow lane.

She suddenly pulled up as we approached a little bridge with white railings and invited us to peer down.

All this talk about blocked ditches had led me to wrongly suppose that the ditch would be piled high with discarded washing machines and supermarket trolleys.

In fact, it was filled with vegetation and branches that had broken off the overhanging trees.

It was hardly an eyesore but water was not exactly rushing in joyous torrents down a silvery brook. "Where is the water? See for yourself," demanded Mrs Cobb.

Underneath the greenery, was the answer. But there was not a lot of it as Mrs Cobb would later prove for our photographer when she volunteered to jump, revealing that the water just about covered her ankles "It has just been terribly neglected," she said. "Twenty years ago you could canoe here from Seacourt Stream. We have begged the Environment Agency to clean out Seacourt Stream."

But it still seemed hard to grasp the idea that such a small ditch could divert thousands of gallons of water in the swollen Thames just before it reached Osney Mead.

"Well, if it worked for 300 years, there is a good chance it will work again," said my guide.

The Environment Agency has itself spoken in the past of the importance of maintaining the streams in this area. The residents, however, suspect they listened and then did precisely nothing.

But why would the EA be in the business of spending many tens of millions to create a channel similar in size to the Thames, when a bit of ditch digging, perhaps involving youngsters on community service, would spare them such colossal spending?

Mr Hanniford reckoned he knew the answer to that - the big bang theory.

"I think that they just want to do something really grandiose. There is an element of vanity and personal aggrandisement. They want to create something massive. It's what they like to call a 'final solution'."

There is, in fact, one simple cause for inactivity on the issue of clearing streams and ditches, as I earlier discovered when talking to the EA.

It centres on the issue of responsibility.

As Marcus Van Someren, of the agency's flood risk management team, explained: "When it comes to the drainage of an area, the responsibility, the clearance and maintenance is down to the landowner. In the case of the area around Binsey, I think it is one of the colleges.

"We appreciate the streams could do with some maintenance. We do encourage landowners to maintain ditches properly. We have power under the Land Drainage Act but it can be difficult to prove within the law that landowners' failure to act has caused flooding."

From Binsey, we headed for Godstow, where large sections of the river bank had been eroded during the recent flooding, with bags of cement visible in the river. "It gets more eroded every time it floods," said Mrs Cobb. "It means Port Meadow holds less water every time it floods. The embankment here needs to be high and sturdy."

But we were here to find the source of the centuries old overflow ditch, marked on so many historic maps.

About 50 yards short from Godstow Lock we stopped at a footbridge. It was the point where water from Port Meadow should overflow into Swift Ditch. It was bone dry.

"You would not know it was a ditch unless, you had seen it on a map would you?" Mrs Cobb asked.

If you follow it inland, as she has, it becomes more marshy but you will also find trees growing in the middle of the ditch.

There can be no arguments that Swift Ditch only now exists in name.

But is it worth going to court and paying a river engineer £1,000 a day to investigate it, as Mrs Cobb is proposing to do?

The Environment Agency, thinks not.

Mr Van Someren said he believed their most vocal critic had lost sight of the bigger picture.

He said: "We are aware of the action Mrs Cobb wants on Swift Dike. But we see the ditch as only part of the stream system all over the Binsey/Port Meadow area.

"If you look at the flood area, Swift Dike is in the middle of it. What is being proposed would merely move water from one flooded area to another. We do not consider it to be part of any flood alleviation scheme for West Oxford. We don't think it would have done anything to ease the July flooding, whatever condition it had been in.

"Our role is to alleviate flooding on a major scale. And if it comes to any civil action, we will have to defend what we do."

With no firm solution of its own on the immediate horizon, perhaps the agency should pause to think whether lawyers or men with shovels will win the agency most friends in the months ahead.