The Liberal party has wheeled out its elder statesman, former prime minister John Howard, in a last-ditch attempt to convince Liberal voters in Wentworth not to punish the government with a protest vote on the weekend.

Polls this week, including the Liberals own internal polling, show that the Liberal primary vote has slumped to 32.7% compared with 62.2% that the former member, Malcolm Turnbull, won in 2016. At this level of support the Liberals would likely lose the seat for the first time in its history – and their one-seat majority in parliament.

During a street walk in Double Bay, Howard experienced first hand the sentiments in Wentworth, with one voter telling him candidly he was appalled by the treatment of Turnbull at the hands of his own party and would not be voting Liberal.

But generally Howard was greeted warmly, if noncommitally, by people in cafes as he sang the praises of Liberal candidate Dave Sharma.

Later Howard told the media: “I want to say to any normal Liberal voters in Wentworth who may be a bit grumpy, who may be a bit disillusioned at this time, you cannot risk a protest vote in the comfort that if you vote against the Liberal party, enough other people will vote for the Liberal party and it won’t matter,” he said.

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“If you’re in that category please don’t romance with the idea that you can indulge with a protest vote and it won’t have any consequences. There is no such thing in modern politics as an unlosable seat,” he said.

Howard warned that losing the government’s working majority would make the last months until the general election due in May “very difficult” and would feed perception that a Labor government is more likely to win the next election.

“I don’t think those normal Liberal voters in Wentworth want a Labor government,” Howard said.

“Certainly if they are living on their savings and they have [opposition leader] Bill Shorten snatching away the benefit of their dividend imputation, then retired people will take a massive tax hit from a Shorten government,” he said.

Howard declined to criticise Turnbull who has been overseas during the entire byelection and has not even given a written word of support to Sharma. But in a veiled criticism, Howard said he personally still owed a debt of gratitude to the party for the opportunities it had given him, which was why he was out campaigning.

In a further sign that the Liberals are worried, they have stepped up their direct mail campaign with new leaflets warning that the election is “50-50” and that voters in Wentworth risk a hung parliament, and that greater uncertainty would mean “a weaker economy and higher taxes for local business, retirees and families”.

The independent candidate Kerryn Phelps responded saying the confusion and chaos in Canberra was of the government’s own making, beginning with its decision to dump Turnbull as leader, triggering the byelection.

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“We now have another leadership spill being suggested in the National party,” said Phelps.

“The government had its senators voting on a motion that it now says it didn’t know what it was voting on. If there is instability its being created by the Coalition,” she said.

Phelps has promised not to block supply and to consider each bill on its merits. She has already been in touch with the two other independents in the lower house, Rebekha Sharkie and Cathy McGowan to learn how they work as independents.

“In terms of no-confidence motions, that would depend on the behaviour of the government. But my intention is that they should go full term,” Phelps said.

Phelps said her campaign had referred an anonymous email alleging she had HIV and was pulling out of the race to the Australian Federal Police.

Sharma said his campaign had had nothing to do with it, and he had personally phoned Phelps to explain that.