Andy Burnham has asked Health Secretary, Jeremy Hunt, to substantiate his claims that the Labour MP hid hospital failings in a "cover up".
He said he was concerned that disclosure rules had been broken and challenged Mr Hunt to apologise.
It is impossible to see how you can claim this mounted to a cover-up," he told him in a letter.
I therefore ask you, by the end of today, to provide me with evidence to substantiate your assertion.
If you fail to provide such evidence, I will require a full retraction and public apology. If that is not forthcoming I will consider further action.
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Owners must also prove they have something to pick up dog mess with under new rules imposed by one council.
The former prime minister made the comments as he prepares to return to politics saying he wants to be "part of the debate" on Brexit.
The new measures would mirror childcare vouchers and see workers sacrifice some of their salary to benefit.