Boris Johnson has agreed to speak to Thames Water over its decision to choose Fulham as a location from which to build part of the super sewer - after a fashion.

The Mayor was challenged over the issue at his London Assembly Question Time by his deputy, Kit Malthouse and, having initially said he would 'swerve' the issue when questioned by Mr Malthouse, Mr Johnson was persuaded to speak up after Mr Malthouse outlined the 'devastating' effect the tunnel would have on the area.

Mr Johnson replied: "I am sure a solution can be found that minimises the impact on the residents of London and that is what I want to achieve. It would be wrong of me now to try to give you a route or to endorse or reject this or that site. I have made representations already and will be making further representations to Thames Water about impacts on Londoners and I am more than happy to discuss that with you and to reflect the views of your constituents."

In a shock decision last month, Carnwath Road in Fulham was chosen in preference to Barn Elms to house a main shaft site, one of several up and down the river that are needed to facilitate the construction of the 20-mile long, £4.1bn tunnel which, in the face of mass opposition, Thames Water says is needed to stop millions of tons of sewage seeping being pumped into the river every year.

Opponents say there are cheaper, less disruptive options.