Senior Conservatives have raised concerns that HS2 will increase the risk of homes being flooded, as the high-speed train line passes through areas affected by the recent extreme weather, runs over miles of high-risk floodplains and will require the diversion of seven rivers.

The Liberal Democrat flooding minister, Dan Rogerson, has admitted the scale of the flood risk associated with HS2 has not been fully assessed for the first phase of the route from London to Birmingham.

The HS2 route crosses more than 100 watercourses, each of which will have a degree of flood risk associated with them, the minister said in answer to a parliamentary question last month.

He said: "The scale of that risk will depend on the precise alignment of the route. At present this has not been fully assessed, nor has an assessment been made for the phase two routes."

HS2 has said it is aiming to avoid an increase in flood risk by using water management techniques and viaducts. But its team has conducted new surveys of the line between London and Birmingham during the recent wet weather.

After the floods, some MPs are demanding more reassurances about the potential affect of HS2 on river and groundwater flooding.

The Conservative minister for Europe, David Lidington, the MP for Aylesbury, has written to cabinet colleague Patrick McLoughlin, the transport secretary, saying his constituents are sceptical about HS2's promise to create protection against floods.

He wrote: "You will not be surprised to hear the residents are very fearful that the construction and operation of HS2 across the floodplain close to their homes will add significantly to the flood risk. It is indisputable that both construction and operation will require farmland to be taken which for now soaks up surface water and which ought to act as natural flood protection for my constituents. People in this part of Aylesbury are sceptical about the assurances from HS2 that they will design in effective flood protection measures."

A former Welsh secretary under the coalition, Cheryl Gillan, has also written to the British Geological Survey to ask for greater reassurance about the potential impact in her Chesham and Amersham constituency, parts of which were recently flooded near the HS2 route.

She said she was surprised at Rogerson's comments that the flood risk has not been fully assessed and wants more answers about how it could affect water resources. Several West Country MPs are now calling for some of the £42bn due to be spent on HS2 to go towards flood protection instead.

An HS2 spokesman said: "During the recent wet weather we have been carrying out visual inspections where the planned line between London and Birmingham crosses watercourses. We will continue with these types of surveys where access has been made available as part of the route development.

"HS2 will be designed to remain operational during a one in 1,000-year flood event. Put simply, that means the railway is being built so that it can withstand just the sort of extreme weather that we have seen up and down and the country recently."

Labour yesterday dismissed "ridiculous" criticism of Barry Gardiner, the shadow floods minister, who was photographed on a beach in Cancun, Mexico, last week while homes were still under water. While Gardiner was abroad speaking at a conference organised by a pharmaceuticals company, Ed Miliband cancelled a trip to India to visit communities hit by the floods.