The Labour leader, who has sought to place the NHS's future at the heart of next year's general election, pledged this weekend that anyone who goes to their GP fearing they have cancer will undergo a test and receive a result within seven days.
But Stephen Pollard, author and editor of weekly newspaper The Jewish Chronicle, wrote diagnosing cancer requires multiple tests and said it was "utter nonsense" to suggest there could be only one.
He said Miliband was either being cynical or did not actually know how cancer diagnoses were made, adding: "In other words, he's just being an idiot."
Mr Pollard was diagnosed with leukaemia two years ago, only because his GP noticed issues with his blood tests, produced as part of another procedure, and sent him for further examination, leading to his diagnosis around a month later.
While he said a diagnosis could be prolonged by "the jaw-dropping inefficiency of the NHS", he said Miliband's pledge showed he was living in a "fantasy world where the NHS could do everything at the drop of a hat".
"I thought I'd seen it all when it comes to political cynicism," he wrote in The Mail On Sunday.
"Look at the long view and all the parties are as bad as each other, making promises they know can't be delivered or pledges they've no intention of honouring.
"But in nearly three decades of following politics, for sheer shameless, dishonourable and downright nasty cynicism, nothing I've encountered comes close to Ed Miliband's promise yesterday that for anyone with suspected cancer, under a Labour Government they will be able to 'go to the GP and within a week you get both the test and the result'."
While the polls for next May's election are close, they show Labour enjoy a commanding lead - 12% according to the most recent YouGov poll - over the Tories when it voters are asked who they trust to protect the NHS.
Mr Pollard wrote: "Mr Miliband has chosen to make the centrepiece of his campaign on the NHS, one of the core issues of the General Election, a pledge on cancer that is essentially nonsense – based neither on medical reality nor patient need.
"Even if there was one overall cancer test that could be delivered within a week, it would be pointless without an NHS able to deliver the right care.
"But instead of focusing on a decent policy, he is the one who is focused on posturing more than principle.
"Here's the cynicism. Labour has a 12-point lead over the Tories on the NHS – and Mr Miliband will do anything he can to keep the issue alive as one of the key battlegrounds of the General Election."
"Even if it means making cynical promises that leave this cancer patient simply nauseated."
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Labour had not responded to HuffPost UK's request for comment as this story went live.
In July, a Labour source close to Miliband told HuffPost UK that the party was "determined to use the NHS of the centrepiece of the summer campaign".
"We want to do more on the NHS. We are trying to give it a greater weight and a greater importance," they said.
In his much-derided conference speech in September, the Labour leader pledged an extra £2.5 billion in NHS funding that would be funded by a "mansion tax" on houses sold for more than £2.5 million.