Theresa May's general election campaign amounts to "no more than a slogan", the first editorial of the London Evening Standard under George Osborne's leadership suggested on Tuesday 2 May.
The freesheet, owned by Evgeny Lebedev, also claimed that the vote to split from the EU last June was a "historic mistake".
"No one should assume that the referendum gave a mandate to the Government to answer any of these questions about Britain's future. It did not," a leader piece read.
"A general election victory for the Conservatives could provide more of a mandate, but only if the Prime Minister and her colleagues spell out in much more detail what their intentions are.
"It's early days, but that is not happening, thanks in part to the failure of the desperately weak Labour leadership to offer a proper opposition.
"There's nothing wrong with repeating election campaign slogans; the problem comes when the election campaign amounts to no more than a slogan. If you ask for a blank cheque, don't be surprised if later it bounces."
The piece, an attack on May's "strong and stable leadership" campaign, comes as the PM seeks to play down a Brexit row with EU Commission President Jean Claude-Juncker as "Brussels gossip".
The dispute apparently started during a Downing Street dinner between Juncker, Brexit Secretary David Davis and May on Friday 28 April.
"The complaints from Brexiteers that these discussions about our future with Europe's governing elite must be kept secret is one of the many ironies that will entertain us in the coming months. The country should prepare for more tough days ahead as reality bites," Osborne's Evening Standard said.
The former Conservative MP and pro-EU campaigner was sacked by May as Chancellor after she succeeded David Cameron in July 2016. Osborne has since gone onto to quit the House of Commons and advise investment fund manager BlackRock.