The Independent has learnt that Mr Mellor put pressure on Sir Ronald Grierson, chairman of the South Bank Board, during the secret selection process to choose between the Philharmonia and the London Philharmonic Orchestra. At the time, Mr Mellor was a Home Office minister and also deputy chairman of the London Philharmonic Trust.
The Mellor controversy has gathered pace since revelations that he had an affair with the actress Antonia de Sancha. It gained ground last week during the Mona Bauwens libel trial against the People, in which the defence revealed that the minister had accepted a free holiday in Marbella at the start of the Gulf crisis, apparently in contravention of ministerial guidelines.
The holiday was paid for by Mrs Bauwens, whose father is chairman of the Palestine National Fund, at a time when the Palestine Liberation Organisation had declared its support for Saddam Hussein.
Yesterday, Mr Mellor's position looked even more precarious when it was alleged that he had been on another free holiday, before the controversial Marbella trip, paid for by Sheikh Zayed, the ruler of Abu Dhabi.
Earlier, criticism was made of Mr Mellor for accepting the use of a pounds 300,000 Mayfair flat - where he had at least one rendezvous with Ms de Sancha - and a pounds 60,000 Mercedes from Chelsfield, a property company headed by Elliott Bernerd - the man who nominated Mr Mellor for his post as deputy chairman of the LPO.
Sources close to the LPO said yesterday that Mr Mellor's attempted intervention in the South Bank controversy was made after rumours circulated suggesting that the LPO would not be awarded the residency.
The selection of a single resident orchestra for the Royal Festival Hall, within the South Bank complex, was carried out by a committee chaired by Sir John Tooley in late 1989.
Three days before Sir John's report to the South Bank was due to be published, in January 1990, word spread among both orchestras that the Philharmonia was to be selected. That night, Mr Mellor called Sir Ronald at home and suggested that plans for a single residency - of which he had previously been in favour - should be scrapped.
If the rumour had proved correct, his intervention would have resulted in the LPO retaining a partial hold on the Festival Hall instead of finding itself homeless.
'Sir Ronald was furious,' a senior source close to the South Bank said. 'The irony is that the rumour was wrong and Sir John Tooley's report was actually recommending the LPO. It would have been the joke of the century if he had taken Mr Mellor up on his suggestion.'
It is understood that Sir Ronald, a close friend of Baroness Thatcher, took legal advice and told his fellow board members. Sir Ronald, who is vice-chairman of GEC, declined to discuss the incident yesterday. 'I do not think any purpose would be served by adding to Mr Mellor's troubles,' he said. But he added: 'You are obviously very well informed.'
Sir John Tooley was not available. Bryan Gould, shadow Secretary of State for National Heritage, said the incident was 'disturbing'. He added: 'Mr Mellor seems to have a disregard for the rules that govern ministerial conduct and a sense in which ministerial power is seen as a weapon to be wielded to secure personally-identified objectives.'
A source with a detailed knowledge of Mr Mellor's phone call to Sir Ronald said: 'Having got hold of the rumour that he was on the losing side, he suggested that Sir Ronald should announce that he was not proceeding with orchestral residency at all and that no one should be appointed.
'It is very very odd that a minister should be on the board of a body which might or might not receive government favours. I am sure there is no law against it but it is a peculiar situation that one would not want to see too much of.'
Mr Mellor and the South Bank declined to comment yesterday. John Willan, managing director of the LPO, said the allegations were 'irrelevant'.
The LPO, whose Arts Council grant was increased from pounds 461,920 to pounds 1,062,000 this year, said Mr Mellor's links have not been an advantage. Judy Grahame, its public relations consultant, said: 'I think that Mr Mellor would have had to have been extra-careful not to have shown favouritism because he had had links with the LPO. If anything this has probably been a disadvantage to us.'
Members of other orchestras disagree. Daniel Salem, chairman of the Philharmonia Trust, said: 'In a way, for Mr Mellor, by going on to the Treasury and at the same time still being connected with the LPO, and at the same time holding the purse strings, there is always the basis for a potential conflict of interest and I don't think this is quite right.'
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