Cory Bernardi has accused Tony Abbott of acting out of self-interest after the former prime minister urged “rebellious” conservative colleagues not to leave the Liberal party.

The former prime minister wrote in the Australian on Friday that Coalition MPs unhappy with the government’s direction should “stay and fight” in the party, saying it was better to “fix it, not to leave it”.

He said it would be a “catastrophic mistake” for MPs to abandon the party and so deliver the opposition “at least two terms” in government.

Abbott’s comments come after the chief Nationals whip, George Christensen, issued a threat last week to leave the Coalition “tent” if the Turnbull government was not more loyal to its voters, amid growing concern that Liberal senator Bernardi is preparing to split as well.

“We don’t owe the party slavish obedience but we certainly owe it respect and loyalty,” Abbott wrote. “If we think the party is headed in the wrong direction or is making a big mistake, our duty is to try to fix it, not to leave it.

“Few people would have more reason than I do to be disgruntled with the federal parliamentary Liberal Party. Yet I want to make it crystal clear: any abandonment of the party would be a catastrophic mistake.”

Bernardi, who has repeatedly talked about the need to create a new conservative force in Australian politics, outside of the Coalition, has fired back at Abbott.

Bernardi wrote on Twitter on Friday: “While most on break only person talking up division in Lib Party this past week is @TonyAbbottMHR. Always back the horse named self-interest.”

Abbott said he has received “literally thousands” of letters, cards and emails of support since he lost the prime ministership last year, and “at least a third” asked him to consider starting a new political party.

“Time and time again, I replied that, for all its faults and failings, the Liberal National coalition is our country’s best hope of sensible centre-right government and that it’s much easier to repair an existing party than to form a new one,” he wrote.

He said any Liberal supporter who thinks the party should be punished for “behaving dishonourably and for emulating Labor’s political execution of an elected prime minister” needs to realise they would be “punishing our country” if they supported a breakaway conservative party, because it would help to elect a Labor government.

“Right now, a combination of unhappiness with what the Liberal party has done to itself and excitement about the Trump insurgency in the United States is driving interest in a new political alignment here,” Abbott wrote.

“It’s entirely possible that an ­explicitly conservative party, ­denouncing the Coalition as ­unprincipled opportunists, could win a Senate seat in every state.

“[But] the bottom line, should rebellious Liberals form a new conservative party, is that decent, well-meaning people will set back the cause they supposedly support, possibly for a generation.”

Any new party would simply leach preferences away from the Coalition and deliver power to Labor, as One Nation had almost done in 1998, he said.