That is the latest stark warning from the Environment Agency, which came to Preston to launch a flood warning system aiming to give at least two hours notice of disaster.

And bosses say that although the worst-case scenario will only happen once in every thousand years, that event could happen at any time.

The latest flood warning zone for the city includes homes across Lower Penwortham and in the Broadgate area of Preston, and gives some idea of the devastation expected if extreme floods hit.

Chris Strong, leader of the flood incident management team based at Walton Summit, said that a rise in the Ribble which would begin to cause flooding in Lower Penwortham is only a "one-in- 75-years" event, while a larger storm which would lead to flooding in Broadgate was a "one-in-100-years" event.

She said: "This whole map area is based on what we call a one-in-1,000 year event – but that does not mean it could not happen tomorrow.

"The key message is that flooding is a risk and people who live in this area should start now to prepare for what they would do if their property was flooded."

Environment campaigners today spoke of their concerns if any new homes are built on the Penwortham floodplain as part of the Riverworks plan.

Jane Brunning, of the Save the Ribble campaign, said: "It is quite clear from this summer alone that we should stop building on flood plains."

The Evening Post revealed details of the new 24-hour flood warning system earlier this month.

The system will be launched in February and residents in risk areas will be sent letters encouraging them to sign up to receive alerts.

The system will contact people by phone, fax, e-mail or pager if a serious flood is expected.

The new danger map should not affect insurance for current homeowners in the flood warning area, because insurers have known about these risks for years, the Environment Agency said.

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