Their move follows a warning from another leading sponsor, philanthropist Vivien Duffield, that she is reconsidering a pounds 5.5m grant.
Chris Smith, the Secretary of State for Culture, has summoned them all to an emergency meeting. The news that Mrs Duffield might pull out was a serious blow, but the disenchantment of Lord Sainsbury and the Floral Trust places the future of the Opera in jeopardy.
Senior Government sources say the philanthropists are trying to put "unacceptable" conditions on their donations - totalling pounds 20m - which could mean the collapse of the Opera's entire rescue plan.
It is understood that they want the Opera House open for 45 weeks a year, rather than the proposed 35, before they guarantee their money and set out a timetable for payment. That would make it necessary for the state to put an extra pounds 15m into the project. The Government and the Arts Council are refusing to inject extra money into the pounds 198m rebuilding programme.
"The implicit threat from the donors is that they will torpedo the whole rescue package if the Government and the Arts Council don't put in significant extra money," a culture department source said. "There is no way we are going to do that, they can go whistle for it ..."
Mr Smith has identified the issue as the one remaining major stumbling block to the rescue package going ahead. He has invited the three donors to a meeting on 2 November to "bang heads together" to put an end to the crisis. Gerry Robinson, chairman of the Arts Council, and Sir Colin Southgate, head of the Royal Opera House, will also be present.
The Government believes it would be "political suicide" to give any more money to a project which is already unpopular and perceived as elitist.Reuse content