In a helter skelter end to a political year not many of the principal players emerge with much credit. This has been an annus horribilis in Australian politics and none more so than for Prime Minister Malcolm Turnbull who has now lost 24 Newspolls in a row, one of his benchmarks for rolling Tony Abbott.

Abbott had lost 30 when Turnbull moved against him. We’ll return to the Newspoll metric.

But first to this weekend’s Bennelong byelection, once held securely for the Liberal Party by John Howard and before him Liberal grandee John Cramer since the seat was carved in 1949 from some of Sydney’s plusher suburbs.

You’d probably have to go back to the Bass byelection of 1975 lost by Labor in a 14.5% swing — this spelled the beginning of the end of the Whitlam government — to identify a byelection as consequential. If the Liberals lose Bennelong tomorrow, Turnbull’s leadership will be in question.

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In those circumstances government nervousness about Bennelong is to be expected. A loss in Bennelong and thus the government’s majority on the floor of the House of Representatives would signal that bets are off on Turnbull’s tenure, or bets are on, depending on your point of view.

You can be sure of one thing: a good dose of schadenfreude among Turnbull’s internal party critics and their enablers in the media would be on show if Bennelong changes hands.

While conventional political wisdom has it that Liberal candidate John Alexander will prevail, the fact that at this late stage real uncertainty surrounds the result is worrying news for the Coalition.

Let’s consider the arithmetic in a seat won on the primaries by Alexander in 2016 with 50.41% of the vote, and nearly a 10% margin on two-party preferred basis.

Say Alexander prevails in this byelection with a 5% swing against him — at the lower end of predictions — the government would continue to argue with some credibility a “win is a win’’.

After all, byelections tend to produce swings of this magnitude against governments of the day, especially ones whose poll ratings are under stress.

However, if the margin blows out much beyond that 5% swing, say in the range of 7%, it will be more difficult to sustain a case this has been an OK result for the government.

If the swing exceeds that notional 7% this will prove a deeply concerning outcome for Coalition MPs, and therefore even more difficult to spin as a “win is a win’’ result.

If Alexander loses then, as we said, bets are off.

Now, a look at the post-2016 Australian Electoral Commission Tally Room results explains why a swing in Bennelong, if it exceeds 5%, or even 7%, will spook sitting Coalition MPs.

Uniform swings don’t happen in elections, but for argument’s sake if there were a uniform swing of 5%, or thereabouts, in a general election, the Coalition would lose 25 seats.

This would include ministers Peter Dutton in Dickson on a margin two-party preferred (TPP) of 1.6%; Ken Wyatt, Hasluck, 2.05%; and Christian Porter, Pearce, 3.63%. If a swing against the government of between 5-7% was registered Christopher Pyne would go down in Sturt where he is on a margin of 5.89%; Speaker Tony Smith in Casey, 6.06%; and Michael Keenan, Stirling, 6.12%.

In a wave election, in which large swings are recorded — as happened back in 1996 when John Howard prevailed, or earlier in 1975 when Malcolm Fraser stormed into office at the expense of Gough Whitlam — a large number of seats can change hands.

This brings us back to the Newspoll issue.

Having lost 24 Newspolls to Labor with no discernible prospect of winning one in the near future, Turnbull is now saying he “regrets’’ having asserted successive Newspoll losses as a benchmark for his leadership putsch.

“I do regret having said it, if only because it allowed people to focus on that rather than substantive reasons, which were economic leadership and governance,’’ he told Miranda Devine of The Daily Telegraph.

Asked for his reaction to Turnbull’s expression of “regret’’ Abbott said on Sky News he would reserve his comments for after the Bennelong byelection.

Watch this space.