Owen Smith has apologised for his “inappropriate” claim that Labour should “smash” Theresa May “back on her heels”.
The Labour leadership contender initially brushed off suggestions that his comment about the Prime Minister - which was not included in the prepared text of the speech - was at odds with his professed commitment to equality.
He insisted he had been using “robust rhetoric” as part of his pitch to defeat Jeremy Corbyn in the Labour leadership contest, before conceding his choice of language may have “backfired”.
Hours later Mr Smith backtracked, with his spokesman stating: “It was off script and on reflection it was an inappropriate choice of phrase and he apologises for using it.”
The former shadow work and pensions secretary earlier vowed to end austerity as part of a “socialist revolution”, with a new wealth tax on the rich and increased spending on the NHS.
In a speech aimed at wooing supporters of Mr Corbyn to back his bid to oust the leader, Mr Smith announced plans to appoint a cabinet-level minister to deliver fair employment, end the public sector pay freeze and outlaw zero-hours contracts.
The Pontypridd MP also pledged a return to the 50p top rate of income tax and vowed to reverse cuts to inheritance and capital gains taxes.
In an attack on Mrs May - and Mr Corbyn’s response to her at Prime Minister’s Questions - Mr Smith said she had the “temerity” to lecture the Opposition on social justice and insecurity at work.
“It pained me that we didn’t have the strength and the power and the vitality to smash her back on her heels,” he said.
Mr Smith also said: “We should be smashing the Tories back on their heels. Their ideals, their values, let’s smash them, let’s get Labour in.
“It’s rhetoric, I don’t literally want to smash Theresa May back on her heels, I’m not advocating violence in any shape or form.”
But pressed on his choice of language he told 5 News: “Perhaps it backfired, but we should have a bit of robust language in politics, I think.”
A spokesman for Mr Corbyn’s re-election campaign said: “We need to be careful of the language we use during this contest as many members, including many female Labour MPs, have said they feel intimidated by aggressive language.
“Jeremy has consistently called for a kinder, gentler politics. We should all reflect that in our political rhetoric.”
In his speech, Mr Smith said his plans were radical but not “pie in the sky”.
Speaking at the highly-symbolic site of the former Orgreave coking plant in South Yorkshire, Mr Smith said he understood the anger of voters which had contributed to the victory for the Brexit camp in the European Union referendum.
Mr Smith said the UK had become a “country where people feel the system is rigged against them” as a result of austerity measures and inequality.
Setting out his wealth tax plan, Mr Smith said: “To tackle the historic inequality that is holding Britain back, I will take an historic step for this Labour Party by introducing a necessary, inequality-busting wealth tax in Britain.
“A surcharge on investment earnings by the wealthiest 1% in our country that would raise an additional £3 billion per annum.
“Theresa May can wring her hands about inequality all she wants - Labour will do something about it.”
Mr Smith said his proposed wealth tax would involve a levy of 15% on “unearned income from investment”, charged on people with a taxable income of £150,000 a year or more.
Under Mr Smith’s proposals the Department for Work and Pensions would be scrapped and replaced with a Ministry for Labour and a Department for Social Security.
He would introduce new wage councils for hotel, shop and care workers, to strengthen terms and conditions.
A modern equal pay act would end discrimination against women “once and for all”.
Mr Smith vowed to increase spending on the NHS by 4% in real terms every year of the next parliament, paid for by the rich through the new wealth tax and the reversal of cuts to inheritance and capital gains taxes.
He also vowed to reverse the “shameful failure” on the lack of new homes being constructed, insisting “we will build Britain out of this crisis”.
In an apparent swipe at Mr Corbyn, he said: “We need a revolution. Not some misty-eyed, romantic notion of a revolution where we are going to overthrow capitalism and return to a socialist nirvana - I don’t know who I’m referring to - but a cold-eyed, practical socialist revolution where we build a better Britain, where we look the country in the eye and say ‘this is possible, it can be better, we can build a better, brighter future’.
“We have done it before, we can do it again. That’s the sort of government I want to lead, that’s the sort of revolution I want to bring.”
Fire Brigades Union general secretary Matt Wrack said: “We welcome Owen Smith’s decision to speak out for working people, but this Damascene conversion must be greeted with caution given that just one year ago he supported the public sector pay freeze, which is now affecting our firefighter members for the sixth consecutive year.
“Jeremy Corbyn has been supporting the trade union movement all his political life and has a well-catalogued history of putting working people first.”