Former prime minister Tony Abbott has intervened in the tense pre-selection battle in Bronwyn Bishop's electorate of Mackellar, backing a rival to his one-time mentor.

Key points: Tony Abbott says he's given a reference to someone "I respect very much"

Tony Abbott says he's given a reference to someone "I respect very much" There is factional brawling over a number of seats and Senate positions

There is factional brawling over a number of seats and Senate positions Mr Abbott wants party to act to prevent lobbyists acting as king makers

In an interview with 7:30 outside his electorate office two days before Saturday's pre-selection, Mr Abbott backed his confidant Walter Villatora, who is contesting the seat.

"I'm not going to make any adverse comments on my colleague, my colleague of very long standing," Mr Abbott said.

"Obviously I do know some of the candidates in the Mackellar pre-selection.

"One I've worked with very, very closely and I respect very much, and that's why I've given him a reference.

"But in the end it's up to the pre-selectors of Mackellar to make what they think is the best choice."

The other main contender in the seat is long-time Liberal Party member Jason Falinski, who has the backing of the moderate faction.

The campaign in Mackellar has been marred by allegations of dirty tactics.

It follows a summer of discontent in the NSW division of the Liberal Party, with factional brawling over a number of seats and Senate positions.

Unlike in other states where there is an open vote among all party members, NSW pre-selections are decided by small groups of delegates that opens the door to factional stacks.

Mr Abbott has added his voice to the push for the party to be reformed.

"In the end let the Labor Party be the party of factions, the Liberal Party should be the party of merit and the problem with factions is decisions are made on the basis of numbers, not the merits, and that's wrong," he said.

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'You can be a lobbyist or a powerbroker but you can't be both'

The simmering anger boiled over at last month's senate pre-selection at Sydney's exclusive Tattersalls Club, when lobbyists Michael Photios and Nick Campbell exercised last-minute proxy votes.

Walter Villatora is contesting Bronwyn Bishop's seat of Mackellar. ( ABC News )

Mr Abbott introduced rules to prevent lobbyists acting as king makers and the former prime minister is calling on the party to better enforce them.

"The point I made ... at the beginning of my prime ministership is that you can be a lobbyist or a powerbroker but you can't be both," Mr Abbott said.

"My understanding is that this is John Howard's position, it's Mike Baird's position, it's Malcolm Turnbull's position.

"It's certainly my position and it should absolutely be the position of the NSW Liberal Party."

Another long-time Liberal member David Miles has risked suspension to speak out against lobbyists being involved in pre-selections.

Mr Miles runs a rival lobbying business and said the industry group prevented members playing such an active role in selecting the candidates they may later seek meetings with.

"If you are playing an active role within a political party at a senior level and you're also then seeking to lobby governments made up of those people that you potentially put there, I think that's a perceived conflict of interest, if not a real one, that our organisation believes best to be avoided," he said.

Mr Campbell declined to comment and Mr Photios did not return calls.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 6 minutes 48 seconds 6 m Tony Abbott criticises the NSW Liberal Party's preselection processes

Zimmerman defends Senate vote

7.30 has obtained an internal Liberal Party memo sent to Senate candidates defending the two men's participation.

"The selection procedure and meeting were carried out in accordance with the division's constitution," the memo stated.

"The failure to give two alternates had no effect."

Liberal Party state president and North Sydney MP Trent Zimmerman defended the Senate vote and the party's processes.

"We are very pleased with our NSW Senate ticket, which includes two very talented women with diverse backgrounds: the Hon. Concetta Fierravanti-Wells and Hollie Hughes, who will continue Bill Heffernan's work representing country NSW," Mr Zimmerman said in a statement.

"Our preselected Liberal candidates represent the broad cross section of the community and the NSW Liberal Party."

In February, former parliamentary secretary Ross Cameron, state upper house MP Charlie Lynn and branch member Juris Laucis were suspended for appearing on 7.30 and urging the party to reform.