Richard Benyon, accused of blocking dredging on Somerset Levels while minister, says critics are looking for scapegoats

A former Conservative environment minister who has been criticised along with the Environment Agency for mismanaging flood prevention has hit back at what he described as "politicians seeking to become armchair hydrologists".

Richard Benyon has been accused by some south-west MPs and the communities secretary, Eric Pickles, of blocking dredging on the Somerset Levels during his period as environment minister.

Writing for the Guardian, Benyon said he was "uncomfortable with those that reach for the easy option of looking for a scapegoat".

In his Comment is Free article, Benyon said: "We should never view all Britain's flooding problems through the prism of one local calamity. If we were to roll out river dredging nationally on a similar scale to what is going to be spent on the Levels the bill would amount to around a quarter of the UK's GDP."

David Cameron himself said this week that the pendulum had swung too far against dredging, but Benyon said the debate on dredging should not be a binary choice, adding: "I am uncomfortable when politicians seek to become armchair hydrologists."

Benyon, MP for Newbury in Berkshire, was environment minister until last summer, and rejected a major grant to dredge rivers on the Somerset Levels partly owing to Treasury rules requiring proof that the benefit would be at least eight times the cost. Downing Street scrapped the rule for the Somerset Levels last week.

The ex-minister was writing as the Met office warned that a "multi-pronged attack" of wind, rain and snow is expected tomorrow, with heavy rain leading to more potential flooding as up to 40mm (1.6 inches) could fall in just six hours, with gusts of up to 70mph. The EA still has 16 severe flood warnings – which mean a risk to life – in place in the Thames Valley and Somerset, as well as 128 flood warnings across England and Wales. About 56,000 households remain without power since Wednesday's storm.

The special cabinet committee that met on flooding agreed to a wider review of the Treasury cost-benefit rules, admitting that the formula tended to favour urban over rural areas due to the greater density of population in towns.

Ministers continued to battle to show they were keeping a grip on the crisis, including sending out instructions that no councils should charge for sandbags, and the costs would be funded by central government.

At one point Downing Street appeared to suggest it was a matter for councils should decide if they wished to charge, but the local government minister, Brandon Lewis, hastily insisted: "The work that councils are doing supplying sandbags is covered by a grant from central government so there's no need for them to charge. Sandbags should be available where they're needed and free to residents."

Ministers are also increasingly worried about the potential implications of the floods for insurance claims, including its own plans to revamp the flood insurance industry from next year. The minister for policy, Oliver Letwin, is due to meet the insurance industry next week to impress on them the need to handle claims quickly.

The insurer Hiscox called on the government to rethink its planned Flood Re scheme, currently going through parliament. It is one of the first insurance firms to raise doubts about the deal negotiated by the industry last summer. Flood Re is designed to put a levy on most households to keep down the premiums of the 2% homes at highest risk.

Hiscox said Flood Re actively excludes one in six households in flood-affected areas, including many properties currently under water in Somerset and the Thames valley. Customers would be at the mercy of the open market, which would mean flood insurance is unlikely to be affordable for many of those excluded.