The mysterious disappearance of a portrait of a Hampstead mayor has sparked fierce criticism of Camden Council’s handling of its treasured art collection.

A hunt for the only known painting of the 1905 mayor of Hampstead borough, Sir George Barham, went cold this week after the council was forced to admit it had lost the oil painting.

The revelation triggered a backlash from local historians who complained council bosses had shown little respect for its prized collection of artworks – thought to be worth millions.

The council holds more than 1,000 pieces including works by David Hockney, Barbara Hepworth and Patrick Caulfield.

Malcolm Holmes, who worked in the council’s archives from 1963 to 2007, said the latest bungle showed the diminishing regard the council had for its archives.

“I’m afraid Camden does not place a high value on heritage and I feel it has got significantly worse over the years,” he said.

“My own department has three fewer members with a collection just as large. The council has had to have cuts, but that department seems to have had more than others.”

In 2002 the Town Hall cleared its walls of all former mayors as it felt the “elderly white men” no longer reflected the borough’s diversity.

Dr Marianne Colloms was carrying out some research on former mayor and owner of the Express Dairy Company Sir George, who lived in Haverstock Hill, when she stumbled across the council’s mishap.

“The council has been entrusted with these valuable works and it needs to be accountable,” said Dr Colloms, from Flask Walk in Hampstead, who has co-authored a number of local history books.

“I find it difficult to understand how the trail has completely died and they are unable to do anything about it. From my way of thinking that is unacceptable.”

Mr Holmes, 67, said the portraits of former mayors had been badly damaged by removal men when they were hauled down and bundled into storage.

He claimed some of the pictures’ labels had also been mixed up as the pre-war oils were carted between archives in John’s Mews, Russell Square.

“They have been moved around and not been well looked after,” he said.

A council spokesman apologised for the loss, but insisted it was the only portrait which had gone missing.

The portrait had been catalogued in 2002, but when a review of its inventory was carried out eight years later archivists found it had gone missing.

The council unearthed documents which suggested the oil painting had been loaned to the College Farm Trust in Finchley, but the loan deal was never agreed and officials at the trust deny any knowledge of its whereabouts.

But the portrait could yet be traced through the Public Catalogue Foundation, which is collecting a digital record of the country’s oil paintings.

Lucy Ellis, the project co-ordinator for Camden, said: “If a public body knows it once had a painting we will take the details, such as the artist and when it was painted, and hope that it will turn up in another collection that we catalogue.”