Mr Cameron had just toured Warwick Road in Carlisle where he spoke to emergency crews and visited the flood-wrecked home of a young family.
The prime minister came to the city just hours after the Cumbria floods were discussed at an 8am meeting of the government’s emergency Cobra committee, which tackles top priority issues.
Asked what he proposed to do in light of the weekend’s floods, Mr Cameron said: “We will look at what has been done, look at happened on this occasion, and look at what needs to be done.
“I’ve seen the flood defences for myself and they are impressive. But it’s difficult to deal with 14 inches of rainfall in 24 hours. We should look at what we’re planning to build, what we’re planning to spend, to see what more can be done.”
Mr Cameron said the Environment Agency had pointed out that the Carlisle flood defences had already prevented two previous floods happening in the city. “So they haven’t been ineffective,” he said.
Mr Cameron reiterated the unprecedented level of rainfall that triggered the disaster, saying it was higher than in the flood of 2005. Yet in some places, there was less flooding than previously.
He said: “We’re going to have to take a bit of time to work out exactly what happened; why the [flood defence] barriers overtopped; and what else can be done.”
Mr Cameron insisted that the Environment Agency had done a “great job” to protect Cumbrian communities but he said more needed to be learned about why the latest floods happened.
The prime minister said his government was currently spending “record amounts” on flood defences.
Mr Cameron said there will be help for home owners fearful that their property may have become uninsurable after multiple floods.
It would be provided by the government supported national FloodRe scheme, a not-for-profit fund operated by the insurance industry and aimed at those who are living in flood prone area, he said.
Referring to the huge scale of the recovery operation now under way, he said: “This is just the start.
“We’re at the recovery phase, rescuing people, helping them get out of their homes. But we will make sure insurance companies pay up quickly.”
The prime minister dismissed a suggestion that emergency services had been hampered by funding cuts.
He said: “They have the resources they need. I’ve been talking to the police, fire, and ambulance crews and they have done a fantastic job.
“It’s also worth praising the voluntary services – the mountain rescue, and first responders, from around the country. I want to pay tribute to the emergency services.
“They’ve done a brilliant job; and they got help from around the country more quickly than before.”
For Cumbria, more broadly, said Mr Cameron, it was essential to get the message across that the county remains “open for business.”
“People should continue to come here,” he said.
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