The government has been warned it must not backtrack on a deal with the insurance industry to boost Britain's flood defences.

Liberal Democrat environment spokesman Chris Huhne said failure to invest during the next spending review could leave householders without flood insurance.

It is thought that under the current spending review ministers are aiming to give increased protection for 100,000 houses.

He warned that if sufficient flood defences were not planned within five years then cover could be withdrawn.

Huhne has now written to environment secretary David Miliband asking for guarantees that ministers will stick to their deal with insurance companies.

He said: "If the government goes back on its promises, insurers are likely to feel no obligation to continue cover for 100,000 homes that are not commercially easy to insure because of flooding.

"It would also send out a counter-productive signal that the government is not taking climate change seriously. We need sea and flood defences together with tougher building standards to withstand more extreme weather events."

Fears over the impact of climate change and the long term cost of renewing Thames flood defences have also prompted concerns that there might not be sufficient cash available for other schemes.

A Defra spokesman said no further announcements on funding would be made until December.