New hard defences would be unsustainable and too expensive to build he said.
"We will protect the high value areas like London," said Balmforth.
"But not the east coast. For key towns and locations here it may be that the only practical solution is managed retreat. That could even apply to Hull."
Balmforth based his thinking on climate change predictions that assumed a temperature rise to 2080 of between 2% and 5% - depending on the amount of CO2 emissions.
"If you take the median of 3.9% there will be 30% less summer rain and 30% more winter rain.Rain intensity will increase by 40% and there will be a 20% rise in sea levels."
Balmforth said that government spending on flood protection would need to be increased eight fold from the current £800M a year to protect all the UK property at risk of flooding, particularly urban flooding as drainage systems overflow.
Balmforth added that the embedded carbon in increased sea defences and storm storage would have a major impact on the 60% carbon reduction target by 2050.
"We are going to have to accept the ultimate, live with the reality, and adapt," he said.
Balmforth's comments drew an irate response from Hull City Council cabinet member Andy Sloan.
"This guy is talking out of his backside if he thinks any national politician would countenance giving up one third of the UK to the sea," said Sloan, the council's member responsible for economy, regeneration, transport planning and also an economics lecturer at Hull University.
"I can't see the US giving up the entire eastern seaboard, which is equally at risk of rising sea levels," he said.
Hull University physical geography professor Tom Coulthard, lead author of Hull City Council's report on this summer's floods, agreed with
Sloan that it was ridiculous to consider abandoning the east coast.
"It is a bit like telling most the Netherlands to abandon most of their country," he said.
"There are 200,000 or more people here, so I don't think it would ever happen."
Coulthard added that Hull was of vital economic importance as Hull and Immingham together make up England's biggest port.