Senior Liberals say a 'miracle' is needed to win Wentworth

Senior NSW Liberals say it will take a "miracle" to win the Wentworth byelection, labelling a damaging email smearing independent Dr Kerryn Phelps as "the final nail" in the campaign.

Sources close to the campaign said the email that falsely claimed Dr Phelps had HIV and was pulling out of the race was "hugely damaging", and had cruelled their chances of holding the seat.

Liberal candidate Dave Sharma called the email "vile" and supported Dr Phelps' demands for its origin to be investigated by the Australian Electoral Commission.

But party sources said the email, alongside the leak of the Ruddock report into religious freedom, would have the desired effect of causing "maximum damage" to the Liberals and portraying the party as "homophobes".

The email also urged voters to only support Mr Sharma and remove Dr Phelps' campaign posters.

In a last ditch appeal, former prime minister John Howard pleaded with disillusioned Liberal voters on Thursday not to "romance" the idea of a protest vote in Wentworth, warning the federal government stood to lose its majority.

The battle for Wentworth: Liberal candidate Dave Sharma and independent candidate Kerryn Phelps.Credit: Nick Moir

"If enough people decide to register a protest vote then the seat could go to an independent and that will rob the Morrison government of its working majority, it will make the remaining months of this term of office very difficult and it will feed the view in the community that a Labor government is more likely at the next election," Mr Howard said.

Mr Howard accompanied Mr Sharma on the hustings in eastern Sydney's Double Bay, where he greeted voters and spruiked Mr Sharma, a former ambassador to Israel, as a "first-class candidate".

In a direct appeal to the perceived high-expectations of the electorate, which has routinely been represented by cabinet ministers, Mr Howard said: "Wentworth wants somebody who matters. It's had a lot of people in the past who have mattered. If you look around, who is the person who can really matter in the future? Dave Sharma."

Since his exit from politics a decade ago, Mr Howard – Australia's second-longest serving prime minister – has transfigured into a party statesman and a symbol of long and stable Liberal government.

Mr Howard's presence, however, also highlighted the absence of the most recent past prime minister and the former member for Wentworth, Malcolm Turnbull.

"I think a lot of people are sad that he’s not any longer the member and any longer the prime minister,” Mr Howard said.

But he called on voters to consider the bylection as a "binary choice" between "a high-taxing left-wing Labor government and a well-led pro-small business Coalition government led by Scott Morrison”.

The seat of Wentworth has been held by the Liberal Party and its conservative predecessors since Federation.

But Dr Phelps is considered a strong chance of defeating Mr Sharma for the seat, with the result likely to be determined on preferences.

However, neither candidate will be able to vote for themselves. Mr Sharma only moved into the electorate after the campaign got under way.

Dr Phelps, who runs a surgery in Double Bay, lived in the electorate until a recent boundary distribution placed her in a neighbouring seat.

Mr Turnbull, who has been overseas for the duration of the campaign, arrived in Singapore from New York City on Wednesday. He will not return to Sydney before the byelection.

He triggered a flurry of media interest on Thursday, when he "liked" a tweet from the Phelps camp questioning his absence from the campaign. But he promptly retracted it after it was spotted by journalists.

He has so far resisted pleas from senior Liberal Party members to publicly endorse Mr Sharma.