Keir Starmer has lashed out at Tory "magic money tree" tax cuts, suggesting leadership candidates had been on "the moon" - but did not rule out cutting taxes under a Labour government.
The opposition leader hit out at candidates planning to take over from Boris Johnson in a speech in Gateshead this morning.
Quizzed by The Mirror, Sir Keir hit out at an "arms race of fantasy economics" in the unfolding Conservative leadership race amid repeated promises of tax cuts.
He said: "We have had this circus in the last few days, £200 billion of uncosted spending commitments.
"Every single Tory candidate making wild spending commitments should tell us precisely where they're getting that money from.
"Is it cuts, if so what are they cutting? If it's borrowing, tell us how much they're borrowing?
"Or is it the magic money tree that they've suddenly discovered having arrived back down here from the moon, where they've been for the last 12 years."
Asked by The Mirror if Labour would be cutting taxes, Sir Keir did not rule anything out - but pledged that promises would be properly costed.
He said: "We won't be making any unfunded commitments, everything we say will be funded and set out."
During his speech setting out the case for change, the Labour leader said: "We need a fresh start.
"And I know you expect me to say this but we won’t get that, from a Conservative Party infected with the chaos virus caught from Boris Johnson.
"Only Labour can reboot our economy and end the cost-of-living crisis. Only Labour can revitalise our public services and re-energise our communities.
"Only Labour can unite the country and clean-up politics. These three tasks will define my Government.
"Because until we address them, we leave ourselves vulnerable to the shocks and crises we have endured this past, long decade."
He said that up and down the country, Brits are struggling with the cost of living and soaring bills, giving the example of a woman named Zoe from Sunderland.
Starmer said: "Britain should be a confident and prosperous nation.
"But at the moment it’s full of people worried about the next bill coming through the letterbox.
"Take Zoe, from Sunderland, just down the road. Like many people, Zoe’s gas and electricity bills have doubled.
"She says: 'I’m struggling to get by. I haven’t managed a full shop for food in over a month. The cost of living is scaring me and the future looks terrifying'.
"I’ve been up and down the country a lot recently – it’s one of the good things about this job.
"And let me tell you: I've heard a version of Zoe's words from almost everyone I have met.
"Her words reflect the reality facing millions of working people in Britain right now."