Tate Gallery pursues #12.5m painting linked to Magnier

London's art world believes that the Irish multimillionaire, Mr John Magnier, is the unidentified owner of a £12.5 million painting which the Tate Gallery wants to acquire.

The campaign to get the painting for the Tate went into overdrive this week when an unnamed benefactor said it was willing to provide £12.5 million to fund its purchase by the gallery.

Joshua Reynolds's celebrated Portrait of the Omai, a painting of a barefoot Tahitian prince, created a stir in 2001 when it fetched £10.3 million at a Sothebys auction, almost double its estimated price. The buyer was a Mayfair art dealer, Mr Guy Morrison, who frequently acts for Mr Magnier, the businessman who runs Coolmore Stud in Co Tipperary. Mr Morrison is thought to have sold it on last year to a Swiss company with links to Mr Magnier.

Speculation at the time centred on the possiblity that Mr Magnier was buying it as a wedding present for his daughter.

Since then the Tate, which had earlier declined to buy Portrait of the Omai from the Howard family of Castle Howard in Yorkshire, has made several overtures to Mr Morrison to persuade his client to sell the painting to the gallery, or at least to allow it to exhibit the work.

The gallery is also thought to have enlisted the support of the Manchester United manager, Sir Alex Ferguson, to encourage his friend, Mr Magnier, to open talks with the gallery. Mr Magnier, along with his associates, Mr J.P. McManus and Mr Dermot Desmond, owns a significant stake in Manchester United.

The gallery's embarrassment at letting the art work slip through its fingers in the first instance has been compounded by the decision of the British Arts Minister, Ms Tessa Blackstone, to block any attempts to ship it abroad. Two years after the auction, it is still being held at Christie's high-security stores in Vauxhall, south London. Some in the London art world believe that this week's promise of £12.5 million to buy it might even be coming from the British government.

Mr Magnier has consistently distanced himself from the original purchase of the painting.

When questioned yesterday, his public relations adviser, Mr Jim Milton, drew attention to a letter published in the Daily Telegraph last November from Mr Morrison who purchased the painting, in which he denied that he was acting for Mr Magnier on that occasion.

However, it is known that Mr Magnier has used Mr Morrison in the past to buy important works of art in London and elsewhere.

In recent years he acquired a large collection of works by Alfred Munning, the 19th-century equestrian painter, for the Irish multimillionare.

Mr Milton said yesterday his instructions were to draw attention to the letter in the Telegraph. He denied that Mr Magnier was in negotiations with the Tate.

Ms Erica Bolton, a public relations executive representing the Tate, insisted that the gallery did not know the identity of the owner of the painting.

"What we know is that Guy Morrison is acting for the owner, and we work through him," she said.

It was "very unfortunate" that the Tate did not buy it directly from the Howard family when it had the chance to do so privately, she added.