Resurrect mansion tax’

secretary said: “I think the mansion tax is something that the Labour Party should continue ... We would continue to explore that.”

Conservative Treasury minister Jane Ellison claimed he had let the cat out of the bag because Labour’s stated tax choice for health spending, a rise in corporation tax, had been spent 12 times already.

When the Evening Standard asked Labour for clarification, a spokesman for Mr McDonnell did not deny that a mansion tax was being considered.

“This is not current Labour policy, and we will set out our plans in the weeks to come in our manifesto,” said the spokesman. “But we are different from the Tories: we believe in a fair tax system and that means no tax rises on those on lower and middle incomes.”

Ms Ellison, the MP for Battersea, said: “Jeremy Corbyn’s nonsensical ideas on raising taxes will worry voters across the capital — Labour remains committed to a tax on the family home which will inevitably hit property across London. In truth, the only way to ensure we continue to invest in our NHS is growing the economy — and only Theresa May can offer the strong and stable leadership required to do that.”

A return of the tax will embarrass senior Labour figures in London, including Mayor Sadiq Khan, who turned their backs on the policy after it contributed to their 2015 defeat.

Former mayoral candidate David Lammy said at the time that it was based on a “caricature of the streets of London being paved with gold”.

Scottish Labour leader Jim Murphy boasted that Scotland’s share of the tax would pay for 1,000 new nurses north of the border. He said that it was a “winwin for Scotland” because 95 per cent of the costs would come from people in London and the South.

However, under 1,000 properties in Scotland were set to pay the tax, compared with estimates of between 40,000 and 90,000 London homes.