Scott Morrison’s ambition to make day two of the election campaign all about a $387bn Labor tax slug has been disrupted by Treasury disavowing the number and Peter Dutton accusing his Labor opponent in Dickson of using her disability “as an excuse’’ for not moving into the electorate.

Morrison hit the hustings on Friday armed with what the government said was new Treasury numbers revealing Labor’s “tax hit on the economy” would be $387bn but, later in the day, the Treasury head Phil Gaetjens confirmed officials had costed Labor measures at the government’s request but had not provided a total, making it clear the calculation was the government’s number.

In a letter to the shadow treasurer, Chris Bowen, who had complained about the politicisation of Treasury, Gaetjens said the department had responded to a request from the government before the caretaker period to cost various measures. The measures were “costed on a standalone basis but with interactions between the individual proposals not taken into account”.

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Assessing the interactions between the measures is a separate piece of analysis that could affect the total. “For this reason we did not provide a total,” Gaetjens said.

Dutton also cut across Morrison’s central message by launching a personal attack on the Labor candidate in Dickson, Ali France, who has a prosthetic limb as a consequence of a vehicle accident. In an interview with the Australian, the home affairs minister attacked France for living outside the electorate.

“There are plenty of people with disability living in Dickson,’’ he said. “A lot of people have raised this with me. I think they are quite angry that Ms France is using her disability as an excuse for not moving into our electorate.”

With disability groups and Labor expressing outrage, Morrison sought to shut down the controversy by saying Dutton’s remarks had been taken out of context.

But Bill Shorten went on the attack, describing Dutton’s jibe as “disgusting”.

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“She never wanted the car crash. She never wanted the amputation,” the Labor leader told reporters. “But she’s a strong person.

“We want more diversity in our parliament. So why is it that … a mother who lost her leg protecting her child is now subject to a personal attack by a scared government minister? I think that is disgusting.”

Morrison spent the morning in western Sydney in the seat of Lindsay, a seat the government hopes to take from Labor on 18 May, and the Coalition has opened the campaign declaring Labor is a risk to the economy, with the Liberal leader telling voters “because Bill Shorten and Chris Bowen can’t manage money, they’re going to come after yours”.

But Shorten, also campaigning in Sydney, said it was inaccurate to characterise Labor’s decision not to proceed with the government’s stage two and stage three tax cuts, which benefit workers on higher incomes, as a tax “increase”, given what Labor was supporting was the status quo. He also pointed out the government was yet to legislate its own commitment.

The Labor leader said he had chosen to “spend scarce and important taxpayer money on educating the kids, on decreasing the out-of-pocket costs of … cancer treatment, rather than spend it on tax loopholes like deductions to accountants for $1m, or property subsidies”.

He said the existing dividend imputation arrangements that Labor has promised to scrap if it wins in May meant “at the moment in Australia we give nearly $6bn in tax credits to people who don’t pay tax”.

“This is called a gift. And it’s a nearly $6bn gift. And it’s going to increase every year. So when we say we’re not going to give the gift any more, that is not a tax increase. It’s just a decision to improve the bottom line of the budget, it’s a decision to fund our healthcare.”

The treasurer, Josh Frydenberg, played down Treasury distancing itself from the $387bn calculation, accusing Bowen of “clutching at straws by claiming Treasury costings of alternative policies are not legitimate”.

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Frydenberg said Bowen had previously acknowledged that not proceeding with the stage two and three tax cuts would have a fiscal impact of $226bn, which was very similar to the Treasury calculation of $230bn. Labor’s costing was done by the Parliamentary Budget Office.

The treasurer said it was self-interested for Labor to complain about Treasury costing opposition policies when it had engaged in exactly the same practice when it was last in government, when Wayne Swan was treasurer.

But Bowen said the clarification from Treasury meant “Scott Morrison has been caught out lying about Labor again”.

“This is a humiliating rebuke and confirms that Scott Morrison cannot be trusted on the economy,” the shadow treasurer said.

“The last six years have seen a determined effort by Scott Morrison and successive Liberal treasurers to politicise and devalue the Treasury and its officials,” Bowen said. “This is bad for Treasury’s reputation as an apolitical economic agency and bad for the important place it occupies in the Australian economy.”