SCOTTISH Tory chief Ruth Davidson has suffered a huge blow to her leadership after her party's most successful fundraiser announced he is quitting his post.

Sir Jack Harvie, who has raised around £16 million for the Conservatives, has decided to stand down just two months after Davidson took over from Annabel Goldie.

Davidson paid tribute to Harvie and said he had "decided to take a more backseat role".

However, a spokesman for Harvie insisted the 75-year-old businessman would "not be playing any role in the party whatsoever".

It has also emerged that grain tycoon Malcolm Scott has "retired" as party treasurer.

Harvie has been the Scottish party's most reliable source of funds for nearly three decades. His legendary "Focus on Scotland" gala dinners helped bankroll election campaigns north of the Border and cemented the party's reputation in the business community.

He also staged £20,000-a-head soirees at his multi-million-pound estate at Mugdock, outside Glasgow, and has played host to three prime ministers – Margaret Thatcher, John Major and David Cameron – as well as three Tory opposition leaders.

Davidson, who defeated MSP Murdo Fraser for the Scottish leadership, had hoped Harvie would continue to direct funds into Tory coffers. She needs money to pay for staff and help implement the shake-up of party structures recommended by the Sanderson Commission.

Funds are also required for May's local government election, while Sir Jack's dinners would also have proved invaluable for the pro-Union side in the referendum campaign.

A senior party source said: "Jack will not be a hard act to follow – he will be an impossible act to follow. Individual donors have come and gone over the years but Jack has always been the dependable and permanent mainstay."

Harvie made a dramatic intervention in the recent leadership election by insisting he would not raise funds for the new centre-right political party proposed by Fraser.

However, he pointedly failed to endorse Davidson either.

Harvie's retirement is the latest financial headache for the Scottish Tories. Irvine Laidlaw, once the party's biggest individual contributor, stopped making donations after a sex scandal involving orgies attended by prostitutes.

His decision meant the Scottish Tories had to vacate their plush offices in central Edinburgh and move to much smaller accommodation.

Malcolm Scott has also donated generously over the years, but he retired as treasurer last week and was replaced by Davidson ally James Stewart, a director of a London-based private-equity firm.

Scott's departure came after revelations in the Sunday Herald that many of his companies had failed to submit either their accounts or annual returns on time.

Stewart is now likely to be tasked with raising funds in Scotland, although it is not believed he has the same reach or contacts as Harvie.

A spokesman for the tycoon confirmed the retirement: "Sir Jack Harvie CBE, the longest-serving and unrivalled fundraiser for the Scottish Conservative Party, has decided to retire from his role. Over a period of 28 years' voluntary service he has raised an estimated £16m for the Tories.

"Sir Jack has thoroughly enjoyed his time as party fundraiser and wishes the Scottish Conservative Party every success for the future."

Davidson said: "At the age of 75 and with decades of long service behind him, Sir Jack Harvie has decided to take a more backseat role but continues to be a valued supporter of the Scottish Conservative Party.

"I should like to thank him for all that he has contributed to the party through the years as well as for his support of me during the recent leadership campaign."

She said the new treasurer, James Stewart, was announced to the party's executive meeting on Thursday night, and added that retiring treasurer Malcolm Scott remains as part of the team.

SNP MP Angus MacNeil said: "Sir Jack's retirement is clearly a blow for the Tories and for Ruth Davidson's leadership.

"With Ruth Davidson taking her political orders from Tory HQ in London, presumably the party will also now get its funding from there as well."