Scott Morrison has refused to answer questions about the sports grants saga, as Labor cites fresh evidence from the former sports minister Bridget McKenzie that she didn’t change the brief and attachments laying out the controversial funding decisions after 4 April, 2019.

On Thursday evening McKenzie revealed she had not made “any changes or annotations” to the 4 April brief approving the third round of sports grants – raising the question of who changed the material before it was sent to Sport Australia on 11 April, and whether the changes had proper legal authority.

Morrison declined to take questions on the sports grants issue at a press conference on Friday. He said he was there to talk about the latest developments on the coronavirus, including a new funding agreement with the states to provide additional health care. “I’m dealing with coronavirus,” the prime minister said.

Speaking on the Gold Coast, Labor leader Anthony Albanese said McKenzie’s statement, which was uploaded to her website after federal parliament had risen for the fortnight, contradicted the prime minister’s account that “it was minister McKenzie who made all the decisions”.

Albanese said the public deserved answers about who had changed the material after 4 April. “Was it the prime minister? The prime minister’s office? Someone else?

“We know that the prime minister’s office made a change early on the morning at 8:46am on the 11th of April,” Albanese told reporters in Coolangatta. “Who made the further nine additional funding grants, with one removed, later that afternoon during caretaker period?

“The prime minister has to answer these questions and answer them very clearly. You can’t have taxpayer funds being allocated, and changed, and swapped around without knowing who was making those decisions.”

Morrison has sought to distance both himself and his office from the controversy, insisting that McKenzie was the sole decision maker and characterising the role of his office as passing on information “based on” representations from MPs.

The Australian National Audit Office told Senate estimates this week the prime minister’s office had requested a last-minute change before the documents were sent to Sports Australia at 8.46am on 11 April, which was the day parliament was prorogued for the 2019 election. But another set of changes were made later that day.

Constitutional law expert Anne Twomey told Guardian Australia on Friday that McKenzie’s revelation raised the prospect that somebody else made late changes to grants without legal authority.

Twomey, who believes the sports grants are unconstitutional and that McKenzie lacked legal authority to make them, said the latest revelation was “bizarre” because it was not clear who made the changes, if not McKenzie.

Twomey told Guardian Australia that even if McKenzie had legal authority, “[if] the minister wasn’t actually making the decision about which of those grants were approved because she made her decision on 4 April and somebody else – whether it be people in her office or whatever – made changes, that would be problematic from a legal point of view.

“If you accept the commonwealth’s view that the minister is the decision-maker, either the minister’s staff as her agents made decisions to approve things after [4 April], which means she made that decision … [or] if they are asserting someone else made the decision, and that it wasn’t legally her decision because they were not her agents, then these actions have been taken unlawfully.”

Twomey said McKenzie’s claims she did not make the changes showed the “enormous dysfunction” of the way the government had handled sports and other grants. She renewed her calls for the government to explain the basis of its claim McKenzie had authority to approve the grants.

Albanese noted that McKenzie and Phil Gaetjens, the head of Morrison’s department who investigated a breach of ministerial standards in relation to the program, a process that ultimately lead to McKenzie’s resignation, are due to appear before a Senate inquiry into the sports grants.

“We actually just need some straight answers about this scandal,” Albanese said.

“What we know is … hardworking volunteers would have spent hundreds of hours of time filling out application forms, thinking there was a level playing field, when in fact, the fix was in.

“It’s taxpayers’ funds. And then there needs to be answers and transparency.”