Lobbyists alarmed at the Trust's increasing business focus campaigned to vote out three finance-oriented board members in favour of those considered more inclined towards conservation and advocacy.

Three board members then resigned – the chairman, former pharmaceutical executive Graeme Blackman; the Trust's finance committee chairman and Deloitte consultant Michael Batchelor; and former education sector executive Des Thornton.

One Trust insider said there had been an "orchestrated campaign" from influential factions and only 5 per cent of Trust members voted. "It's more than an unhappy time. It's catastrophic," he said.

On the Trust website, Dr Blackman said of his resignation that his "personal distress on behalf of my colleagues and frankly, also the senior management team, at the way a very biased and aggressive campaign to remove three outstanding sitting directors has been carried out, leaves me no option".

"I simply could not work with a board whose priorities I did not heartily endorse."

Dr Blackman also wrote of "deep disquiet among some directors about the processes that led to the election results".

The board members voted out – Andrew Bird, David Beatty and Dominic Romeo – had been members of the Trust finance committee.

The committee had helped steer the trust to a surplus of $1.1 million in 2014-15, after an operational loss of $1.57 million in 2006-7.

Ahead of board elections on Saturday, heritage architect and Trust consultant Nigel Lewis wrote to colleagues saying the future of the Trust was at a crossroads.

"It has downgraded its advocacy role, once its core activity," he said, despite in the past having "led the campaign to the government to introduce policies for urban conservation and historic buildings protection".

Mr Lewis suggested members vote for Christina Dyson, Jock Murphy, Wendy Brooks and Jacqueline Healy -- whose occupations are heritage consultant, former librarian, philanthropic consultant and museum curator.

The Age has also seen a letter that board member Kristin Stegley wrote to members, asking that they also consider voting for the quartet. She called for "revitalisation" of the Trust "with respect to heritage advocacy and conservation".

Trust member Amanda Milledge forwarded Ms Stegley's letter on to her own contacts, adding that she agreed that the trust had become too business like and was losing touch with the community it served.

One of the board members voted out, real estate agent Dominic Romeo, said he didn't understand how "some amazing talents in finance that were instrumental in driving the National Trust into a profit" through initiatives such as the Phryne Fisher exhibition at Rippon Lea and the pop-up bar at the Old Melbourne Gaol would be voted out.

Como House, which is a National Trust property. Photo: Craig Abraham

National Trust of Victoria chief executive Martin Purslow said that delivering the board's strategy had led to its most successful two years, with profit from record attendances at properties such as Rippon Lea House, Como House and Barwon Park.

He said the Trust gets little government funding and had achieved what it had due to a "sustainable business model, and we would like to continue with that sustainable business model".

Mr Lewis did not want to comment and Ms Stegley did not respond to a request for comment.