A pledge by Lord Ashcroft to donate up to £5 million towards a new royal yacht to mark the Queen's Diamond Jubilee was described as "brilliant news" by the project's organisers today.
The former Conservative Party deputy chairman has said he will contribute the seven figure sum to the charitable trust trying to raise £100 million to build a national flagship.
Retired Rear Admiral David Bawtree, who is chairman of the trust, said he hoped the financial gesture would encourage other individuals to come forward.
In a statement on his website Lord Ashcroft said: "The murmurings this week of a privately-financed replacement for Britannia are hugely heartening, even if there is a very long way to go to make this happen.
"But I would like to be one of the first to offer tangible support to the concept, by offering up to £5 million towards the construction costs of a new, effective and flexible royal yacht."
The proposed sailing ship - 650ft long and as tall as St Paul's Cathedral - would provide education and vocational training for young people, facilities for scientific research and a venue for trade missions and commercial exhibitions as well as staterooms for the use of the Royal Family on trips around the United Kingdom and overseas.
Rear Admiral Bawtree said: "I think this is brilliant news for the thousands of young people who are going to benefit from the ship.
"I hope his gesture encourages other individuals and corporate donors to come forward and help us."
He added that he had not been contacted by Lord Ashcroft but looked forward to meeting him in the future.
Lord Ashcroft added that any new royal vessel could be used by other members of the monarchy.
He said: "In addition to the support of the Queen's long-standing and continuing work for Britain and for the Commonwealth, a new royal yacht will underpin the increasingly significant work of his royal highness the Prince of Wales, their royal highnesses Prince William and Prince Harry, and other members of the family.
"A new royal yacht should most certainly be placed at their disposal, and it is right that this should be financed by donations, rather than tax."
The Prime Minister has offered his support to the project and described it in a letter to the Rear Admiral, written in October, as a "splendid idea".
David Cameron's official spokesman said earlier this week the PM would "react favourably" to requests for Government assistance, but believed it would be "inappropriate" for taxpayers' cash to be used on the project.