The chief of the UK's largest trade union will urge his members to back a 'remain' vote at the EU referendum, despite admitting the position will be "difficult" to get behind because of David Cameron's own pro-EU stance.

Unite general secretary Len McCluskey will warn UK workers would be worse off if Britain voted to break away from Brussels at the 23 June ballot. McCluskey, an ally of Labour leader Jeremy Corbyn, will also call for the end to "eye-watering" austerity policies across the continent.

"I'm a supporter of the EU but when I vote for Britain to remain in the EU in June, I will not be voting for the status quo – let me be clear about that," the trade union boss will declare. "I will not be voting for the EU which has sought to impose eye-watering austerity, at the expense of the ordinary citizen not the rich, but on Ireland, Greece, Spain, Portugal and elsewhere. I will not be voting for the EU which is seeking to stitch-up a pro-big business trade deal – TTIP – behind the backs of the people of Europe."

McCluskey will add: "Above all, I will not be voting for David Cameron's renegotiation package – a deal designed to protect the financial interests in the City of London which control the Conservative Party and to pander to anti-migrant and anti-welfare sentiment.

"It is disappointing to see how eager European governments were to accommodate him, in stark contrast to the reception given to premier Tsipras of Greece last year."

This is what you really need to know about the Brexit vote IBTimes UK

How are unions voting?

The comments, delivered at the German ambassador's residence in London, will come ahead of a 14 March meeting between Unite's executive on the issue of the EU referendum. The ruling body will decide the position of the 1.4 million strong union at the talks.

The Trades Union Congress and the GMB Union have thrown their support behind a 'remain' vote at the referendum, while Unison is set to hold a major referendum of its members on the issue in March.

A source close to the Public and Commercial Services Union suggested to IBTimes UK that the organisation could remain neutral on the vote, replicating its position at the 2014 Scottish independence referendum.

But the Rail, Maritime and Transport Workers (RMT), Associated Society of Locomotive Engineers and Firemen (Aslef) and the Bakers' Union are campaigning for a Brexit ahead of the EU referendum.

Labour Leave, a Eurosceptic group set up by Labour donor John Mills and some of the party's MPs, are hoping to win over more trade unionists to their anti-EU side.

The latest opinion poll from YouGov, of more than 1,600 people between 2 and 3 March, put 'remain' three points ahead of 'leave' (40% versus 37%), with 18% of respondents undecided.