Sue Roaf, whose home in North Oxford was the country's first eco-house, is to quit her post as a city councillor.

But she does not intend to resign until local elections next May, much to the relief of the ruling Liberal Democrat administration, whose ranks are already depleted by a number of defections.

Ms Roaf has been appointed Professor of Architectural Engineering at Heriot-Watt University in Edinburgh.

The Liberal Democrats are no longer the largest group in the council and Ms Roaf said she would stay on as councillor for Wolvercote until the elections so that her resignation did not force a by- election.

Ms Roaf said she planned to move to Edinburgh to take up her post after Christmas, but added that she would not sell her eco-house in Blandford Avenue, North Oxford.

Speaking from Fort William in Scotland, where she is writing a book on low-carbon buildings, she told the Oxford Mail: "When I am in Edinburgh I hope to do more research into fuel poverty and temperatures in housing, and I will be pioneering low-carbon buildings.

"My house featured the first voltaic roof in the UK and the world has changed a great deal since I joined the council in 2001.

Ms Roaf said she would continue to represent her constituents until June in order to avoid a by-election.

At present, the Lib Dem administration only has 15 of the 48 available seats.

This follows a number of high-profile defections. Paul Sargent and Tia MacGregor became independent councillors before joining the Conservatives.

John Goddard, leader of the city council, said Ms Roaf's move to Edinburgh would not affect the way the council was run or her role as a ward councillor.

He added: "Sue has told me that she will be in Oxford for half the week and will be able to attend major meetings."

Bob Price, leader of the council's Labour group, said: "You have to question whether the people of North Oxford will be getting effective representation if Sue is spending half her time in Edinburgh."