A £1.5million extension of Burnley's 12th-century Towneley Hall art gallery and museum has prompted an historical debate after claims that the grand old building has been "ruined".

Former Lord Lieutenant of Lancashire Sir Simon Towneley will officially open the extension to the historic hall next Friday.

A visitors' book requesting comments about the extension and explaining the work in detail has prompted many positive comments about the hall in general but the only two remarks on the new building are critical of the structure.

Historians, however, have praised the structure, saying it will weather in time.

The extension has been paid for by a £1.1million grant from the Heritage Lottery Fund secured in 1999 and further money from the Fairclough Bequest and the Lancashire Tourism Partnership.

Although the wing originally existed, it is now connected to the hall by a modern-looking glass-panelled corridor and the new stone contrasts sharply with the weathered look of the hall's faade.

In addition, windows on the rebuilt wing are different to those on the hall which are leaded or sub-divided into smaller sections. One of the visitors' comments said: "I feel very sad visiting here today - columns on the extension!! Fortunately I have my childhood memories."

Another said: "I think you have ruined it. You should have left it like it was, so people can learn more and tell their parents what it was like."

When the plans for the Grade I listed building were shown to councillors in September 2000 Coun Roger Frost, speaking as chairman of the Burnley and District Civic Trust, voiced concerns about them.

Although the civic trust did not oppose the plans, Coun Frost described the glass link between the hall and the new building as "not appropriate to the site".

Today he said he could understand people's concerns about the building's appearance and admitted it did stand out.

He said: "We are not hugely happy with the design but alterations have been made after I made the comments and that has made the design better and more acceptable.

"I think what you see now is a new building juxtaposed onto something 600 years older and in a bit of time it is likely the new building will blend in a little bit more with the original hall."

He said the hall was a complex design of a multitude of styles which had been developed over the years and so there was not one set design to be carried through to the new extension.

He did believe that the facilities inside the new wing would be a boost to the hall and he was considering booking the new lecture hall for the civic trust.

The new wing includes multimedia and audio displays, improved lighting, two lifts to the art galleries and signs to complement and expand the existing displays. It also has a shop, library, education room, offices and toilet facilities.

Susan Bourne, curator at Towneley Hall, said: "The cash from the Lancashire Tourism Partnership has been a great help and will ensure visitors will have a first-class day out whenever they visit Towneley Hall."

Historian James Howell said: "It is as good as it could be, but because of the colour of the stonework it is not the same as Towneley Hall but as time goes on the new building will weather and will become more like the old building."

Fellow historian Ken Spencer said: "Towneley Hall was bursting at the seams and something had to be done. Architecturally I am very pleased with it and I do hope before long they will be opening it again on a Saturday."

English Heritage's assistant director for the North West, Henry Owen-John, said a good 21st-century structure which respects the original old building is better than a poor imitation.

He said: "We feel a much-needed new facility for the hall has been provided."