Johnson casts doubt on thousands of prospective new homes with call to stop building on flood plains during campaign visit to Derbyshire

Nine per cent of houses are built where there is a 'high probability' of flooding – with 10,000 currently in the pipeline

Boris Johnson has thrown housebuilding plans into confusion, by suddenly calling for an end to construction on flood plains.

Around 9 per cent of new homes in England are built on land where there is a “high probability” of flooding – and a recent investigation found that 10,000 are currently in the pipeline.

But, on the campaign trail in flood-hit Derbyshire, the prime minister said: “We've got to stop building on flood plains. We've got to stop building on areas which are vulnerable to flooding.”

Mr Johnson was put under pressure from a worker in Matlock, a few weeks after swathes of Yorkshire and the Midlands were devastated by severe flooding.

He said he had “a huge amount of sympathy” for residents who had suffered, adding: “It's incredibly distressing when that happens.”

However, a ban on building on flood plains would have huge consequences for ambitious targets to construct more homes and tackle the housing crisis.

The most recent statistics show that 9 per cent of new residential homes were built in areas defined as ‘National Flood Zone 3’, by the Environment Agency.

Those are sites with a “1 in 100 or greater annual probability of river flooding”, or half that risk of flooding from the sea.

The prime minister ran into difficulties at the start of the campaign, when he was heckled by flood-hit residents who shouted “Where’ve you been?” and “You took your time”.

The government was strongly criticised for a slow response to the flooding in Yorkshire and the Midlands, which claimed one life.

In Matlock, Mr Johnson said the government was spending an extra £4bn on flood defences, adding: “We will also be making sure that we invest in brownfield sites that will enable us to build the housing that our people need.

“The other thing we've got to do, we've got to put in long-term flood defences, but we've also got to be planting millions and millions more trees.

“It sounds crazy but it's true, you need to plant 30 million more trees on higher ground to deal with the water that is building up.”

Last month, a Greenpeace investigation found that almost 10,000 new homes are set be built on some of the most flood-prone areas of England, including in Sheffield and Doncaster.

More than 5,000 homes have been proposed in high-risk zones of Lincolnshire, where roads and thousands of acres of farmland were flooded in November.

Doug Parr, Greenpeace's chief scientist, described the plans as “literally planning for disaster”.

“Flooding has been flashing on the radar as one of the major impacts of the climate emergency in the UK for years,” he said, “yet our planning system keeps failing to properly recognise it”.