Massimo Prelz Oltramonti resigned his trusteeship in January this year after disagreeing with a decision by the other trustees, including Michael and Isobel Estorick, to sell Melanconia, a 1912 painting by Giorgio De Chirico estimated to be worth £8m. It is thought that the painting will be sold to a US collector.

A spokeswoman for the Estorick said that the painting is being sold to create an endowment for the care of its collections and for further acquisitions focusing on the Futurists.

On this basis, the Museums, Libraries and Archives Council (MLA) has determined that the sale does not breach accreditation standards.

A spokeswoman for the MLA said that the disposal is for sound curatorial reasons because the painting is Modernist, not Futurist, and because any proceeds from the sale will be used to buy further Futurist items or to care for collections projects.

However, Prelz Oltramonti said: 'It is true that it is not a Futurist work, but there are Modigliani drawings and other works in the collection that
are not Futurist. The sale is dressed up as a way of creating an acquisition fund, but in reality it is going towards running costs.

But the running costs are not that high and to raise that money should not be difficult with some hard work. It is unacceptable that such an important piece of art is being sold when the trustees are doing so little to find alternative forms of funding.'

According to the Estorick's accounts for the year ending 30 June 2006, the museum's income was £299,768 compared with £310,838 running costs, while it was left with £481,548 in its reserves. In 2005, Michael and Isobel Estorick gave £98,141 of their own money to the foundation.

The MLA and the Museums Association (MA) are in disagreement over the sale, which contravenes the MA's code of ethics. Caitlin Griffiths, the MA's adviser on professional issues, said: 'There may be curatorial reasons for this sale, but it seems to be a financially motivated disposal.

'Accreditation is the minimum standard and the code of ethics is the higher standard, but the aspiration is that all accredited museums would meet this higher standard. We need to sit down and decide whether changes should be made to accreditation in the light of this.'

In any case, the MLA decision appears to be in breach of its own accreditation guidelines on disposal, which stipulate: 'Decisions to dispose of items will not be made with the principal aim of generating funds.'

The sale may also breach the Estorick's Heritage Lottery Fund (HLF) agreement, which saw a grant of £650,000 towards housing the collection at the museum's London home.

It was given on condition that the ownership of 11 works, including the De Chirico, be transferred from the collection's US foundation to a newly established UK foundation. Now, it seems, one of those works may be on its way back to the US.

Patrick Steel