Planned defences along the length of the flood-hit Thames Valley were delayed and downsized after government funding cuts following the last election, the Guardian can reveal.

The schemes, totalling millions of pounds, include projects near Heathrow, near David Cameron's country home in Oxfordshire and in the constituency of the minister who oversaw annual flood budget cuts of almost £100m.

West Drayton, near Heathrow, the scene of significant flooding in west London, was in line for £2.8m of funding to build up concrete and earth bank defences by 2014-15. But following budget cuts, the Arklyn Kennels scheme was downgraded to a £1m scheme and delayed until at least 2018-19.

At Penton Hook, on the Thames near flood-affected Staines in Surrey, a £5.6m dredging scheme was due to be completed by the end of March 2014, but has received just £2m to date. The scheme was also intended to clean up a site where contaminated silt dredged from the river was dumped.

The government's official advisers, the Committee on Climate Change, calculate that the hole in the government's flood defence funding will result in £3bn of otherwise avoidable damage, but the Guardian has been the first to reveal the specific schemes affected by budget cuts.

The missing schemes were identified by the Guardian by comparing the flood defence spending plans for 2010-11, the final year of the last government's budget and a high-water mark for flood defence spending, with the plans for subsequent years under the coalition.

Lord Krebs, of the CCC, told the Guardian that ministers had been clearly warned of the consequences of the cuts. "The bottom line is that the Environment Agency said loud and clear that if we are going to keep the risk of flooding at the current level, we need an extra £500m during the spending period from 2011 to 2015," he said.

"So are we spending enough on the defences at the moment? No, not if you want to keep the risk at the same level."

The wettest weather in England for at least two centuries has seen the Thames and its tributaries experience their highest flows in generations. River levels will remain high for weeks, fed by saturated aquifers.

Another scheme at Poyle, within a few hundred metres of Heathrow, was in line for £375,000 by 2013/14 but has received just 6% of this so far and has no current prospect of funding.

By Gatwick, a £13.4m scheme to build bigger dams and reservoirs on the Upper Mole river has been delayed by at least three years. The project would also have benefited 3,000 homes in the area.

Upstream from the Thames from London, further flood defence schemes have been affected. At Pangbourne in west Berkshire, a £222,000 scheme to prevent a repeat of burst river banks has received just £15,000 and the number of homes moved out of the higher flood risk categories has been cut from 123 to 23.

At Thatcham, also in Berkshire and in the constituency of Richard Benyon, floods minister from 2010-13, a £500,000 project was delayed by a year.

In Oxford, £1.5m of "short-term" flood protection work was meant to end in spring 2012, but less than £1m has been spent and the works are still incomplete. Further afield in the Thames Valley, and just 10 miles from Cameron's constituency home, a £1m scheme at Moreton-in-Marsh had an end date of spring 2013. The project, to protect 265 homes at "very significant or significant risk" of flooding has had only half the funding to date and no further money is expected.

On Monday, missing or delayed projects were revealed in the heart of the flood-stricken Somerset Levels and at Dawlish, where the main line railway to Cornwall was washed into the sea.

A spokeswoman for the Department for Environment, Food and Rural Affairs, which provides the funding for flood defences, said: "We have spent £2.4bn on flood management and protection from coastal erosion over the past four years. We will continue to build defences where they are needed."

The Environment Agency chairman, Chris Smith, said: "The agency works within clear government guidelines on where to spend the funding it is given." The EA have identified 477 projects costing £2.25bn that would better protect 51,000 homes across England, but these have no prospect of funding before 2019-20.

Maria Eagle, Labour's shadow environment secretary, said: "Now that full details of the flood defence projects that had to be scrapped or delayed are known, it's clear just what a disastrous mistake David Cameron made when he took the short-term decision to axe £100m from flood protection budgets in 2010."

Friends of the Earth's Guy Shrubsole said: "These revelations are further proof that the government hasn't been taking the risks of climate change nearly seriously enough. David Cameron accepts that climate change is increasing flood risk – but he's made the false economy of cutting flood defences."

The government's own scientists have identified rising flood risk as the greatest impact of climate change on the UK, while the Environment Agency states that every £1 spent on flood defences saves £8 in avoided damages.