Labour voters should use the European Union (EU) referendum to give the Government a "punch in the nose", Frank Field said as senior Opposition figures clashed over the referendum.

The ex-minister, one of a handful of Labour MPs backing the "Leave" camp, warned the party leadership's pro-EU stance was pushing supporters who wanted to put "our people" first into the hands of Ukip.

He also appealed to all Labour voters to use the June 23 vote to topple David Cameron from power, arguing the Prime Minister and other senior figures could not remain in charge if they lost.

"Labour voters will know that voting to leave will also result in a change of the leadership of the Government. The two are actually linked," he said after a speech in London.

"If you want to have a pop at the Government, you don't have to wait for the general election.

"We increasingly see that the Remain campaign is the Government's campaign and I think that would be another reason why good old Labour voters will come out and give them a nice friendly punch on the nose."

He criticised Jeremy Corbyn's public "conversion" after years of Euroscepticism and dismissed as laughable Alan Johnson's claim a Yes vote on June 23 could be more important than the election of the 1945 Attlee government.

Mr Johnson - who is leading the Labour Remain campaign - issued a rallying call to unions to support EU membership as the best way of protecting workers' rights.

In a speech to the Usdaw union conference, he said it would "keep the swivel-eyed alliance of the right of the Tory Party and Ukip off our rights at work".

Mr Field responded: "We now have what is surely the most attractive figure on the Remain side trying to tickle us into submission by proposing something that if you asked pollsters to look at it ... the laughter would be so great."

He said he believed Mr Corbyn - who had a long record of Euroscepticism - had come out for Remain because he wrongly feared a challenge to his leadership if he declared for Leave.

"Jeremy's leadership is totally safe because we have no credible alternative," he said.

The position meant large swathes of Labour voters were being made to feel it was not "respectable" to want to leave the EU over concerns about immigration - meaning they would be lost to Ukip.

It was vital to convince voters who had been "on the receiving end" of the impact of increased migration from eastern Europe that they go to the polls voting "Leave" as Labour voters, not as renegades to Ukip", he said.

"Do politicians - enough of us - clearly represent views that see that our people should be first in the queue, and not others? It is around that issue that many people will actually vote," he asked.

"Unless the minority in the Labour Party of MPs who support the leave campaign are able to convince Labour voters that their views are a totally legitimate set of views to hold and - while represented by few in the Parliamentary Labour Party at the moment - it is totally respectable not only to express those votes but to deliver those votes on referendum day, we will deliver to Ukip the next tranche of Labour voters to such an extent that come 2020 our base of support in the electorate will not be strong enough for us credibly to make an appeal for power."

Mr Johnson - and shadow business secretary Angela Eagle - visited BAE Systems in Samlesbury, Lancashire, to highlight industry support for remaining in the EU.

BAE chair Sir Roger Carr was among business leaders who signed a letter in support of remaining in the EU in February.

Unite general secretary Len McCluskey said: "What's at stake with this referendum is huge. It is the biggest vote we have faced and will determine this country's future.

"So when leading manufacturers are on the side of remaining as a full and engaged member of the EU, we listen.

Mr Johnson told the conference the party was "united" behind the Remain cause, with unions representing four million workers now signed up.

Post-war Labour politicians " rose to the challenge of their age and they secured a peace in Europe that has lasted for over 70 years", he said.

"It's our job to ensure that the great post-war vision of our predecessors is not diminished and undermined by those whose vision of Britain is as an offshore, regulation free, anything goes economy engaged in a race to the bottom.

"I believe that the referendum on June 23 is every bit as important as that election in July 1945. Perhaps more so.

"It is a vote about whether Britain remains in or leaves the EU, and there will be immense consequences for everyone here, and for every family in the land.

"But it's about more than that. For me, it's about what kind of country we are, what kind of society we want to be."

The vision of pro-Brexit campaigners such as Michael Gove and Boris Johnson was of " a small state with few, if any, workplace rights" - removing protections secured via Brussels.

"They know the EU protects workers' interests, and it's one of the principal reasons why they want to leave".

MPs have agreed to formally discuss a petition, backed by more than 200,000 signatures, that was launched in protest over the Government's decision to spend more than £9 million on sending a pro-EU leaflet to all UK households.

A debate will be held in Westminster Hall on May 9, the Petitions Committee announced.