The Virgin And Child With Saint Anne by Leonard da Vinci which two French experts believe is too bright now it has been 'over-cleaned'

Even in the painstaking world of art conservation, there can have been few more delicate tasks.

The £160million Virgin And Child With Saint Anne by Leonard da Vinci was in need of a clean-up.

But an attempt to restore the 500-year-old Renaissance masterpiece has descended into an unseemly row, with two British art experts accused of being too zealous.

Concerns have been expressed that the painting has been overcleaned, leaving it garishly brighter than Leonardo intended.

British conservation experts Luke Syson and Larry Keith were reportedly the most insistent members of the 20-strong international committee which advised the painting’s owners, the Louvre, to carry out the cleaning process.

While the programme of restoring The Virgin And Child With Saint Anne is not yet complete, two senior French art historians have already resigned from their positions on the advisory committee.

According to reports, they did so to disassociate themselves from the cleaning techniques being used.

Mr Syson, curator of pre-1500 Italian paintings at the National Gallery in London, and Mr Keith, director of conservation at the National Gallery, were yesterday unavailable for comment.

The pair both worked on the British gallery’s current blockbuster Leonardo da Vinci exhibition, which does not feature the Louvre painting.

A spokesman for the Louvre has, meanwhile, insisted that the cleaning was one of the best researched ever, and that all had gone well.

The Parisian gallery has not commented on the resignation of Ségolène Bergeon Langle and Jean-Pierre Cuzin.

The two conservation and painting experts have also declined to comment except to confirm their resignations.

But a Louvre source said the specialists believed the painting had been overcleaned, and that more tests should have been carried out first.

Remaining members of the committee were said to be split between those who fear the painting has been made too bright, and those happy with the work.

Mr Syson and Mr Keith are among the members believed to be satisfied with the ongoing restoration.

The Louvre source was quoted in the Guardian newspaper as saying: ‘The English were very pushing, saying they know Leonardo is extremely delicate but “we can move without any danger to the work”.

'There was a row a year ago about solvents because they said they were safe, and Bergeon Langle said they’re not safe.’

Fresh developments may come next Tuesday, when experts are due to view the masterpiece to assess the conservation process. They may decide retouching is needed.