The £10m plan to restore a Mackintosh masterpiece has made a major move - of nine centimetres.

The effor to restore the Willow Tea Rooms building in Glasgow's Sauchiehall Street has taken the small but significant move forward, by moving a key window back to the position originally intended by the Scottish architect, designer and artist.

The window of the Salon de Luxe, perhaps the most famous room in the tea rooms, has been returned to its original position by builders working for the Willow Tea Rooms Trust, which is undertaking a major restoration of the building.

The window had been moved at some point in the building's long life since it was first opened in 1903.

The window was moved, it is believed, by Daly’s Department Store after they purchased the site in 1927.

As part of the Trust’s restoration project it has been carefully moved back in place, as has the window below it, on the ground floor.

It has also been revealed that, after a copyright dispute with the owner of the Willow Tea Rooms, Anne Mulhern, who now runs the tea rooms with that name at the nearby Watt Bros department store, the building, and its adjacent new education and training space, will be called Mackintosh At The Willow.

Pamela Robertson, Professor of Mackintosh Studies at the University of Glasgow, said: "Moving the Salon de Luxe window back to its original position is an integral part of the project to restore the Willow Tea Rooms to their former glory.

"It is seemingly a small change, but significant in showing the level of care being devoted to the project and the Trust’s aims to make this restoration as accurate as possible."

Moving the windows is a key part in the eighteen-month project that plans to be completed in time for the 150th anniversary of Mackintosh’s birth in 2018.

Professor Robertson continued: "The Salon de Luxe was undoubtedly the most luxurious and glamorous room in the Willow.

"It cost visitors an extra 1p to enjoy their cup of tea in the room. When restoration is complete, visitors will once more be able to enjoy the beautiful Mackintosh interiors.”

Celia Sinclair, founder of the Willow Tea Rooms Trust, said: "The aims and objectives of the Trust are to restore and preserve this iconic piece of Glasgow’s heritage for the benefit of the general public.

"Our hope is that it will educate, inspire, encourage art, creativity and entrepreneurship by informing local and international visitors about the architecture, design and artwork of Charles Rennie Mackintosh as well as the business, social history and success of Catherine Cranston."

The Willow Tea Rooms opened on the 29th October 1903.

The building is now in the ownership of the ‘The Willow Tea Rooms Trust’, a registered charity.

Simpson & Brown were appointed as Conservation Architects and lead Design Consultants to restore the Willow Tea Rooms. The Trust has been supported by The Monument Trust, The Heritage Lottery Fund, Historic Environment Scotland, Glasgow City Heritage Trust, Glasgow City Council, Dunard Fund and Architectural Heritage Fund.

To restore the interior and create the education, skills and training centre the Trust needs to raise a further £2.5 million in match funding from the public, Charitable Trusts and public sources.