A Brexit vote at the EU referendum will benefit Boris Johnson and his pursuit of power, Matt Wrack warned, as his union threw its support behind the Remain campaign on 12 May. The 37,000-strong Fire Brigades Union (FBU) is the latest in a growing list of trade unions joining the battle to stop the UK breaking away from Brussels.

"It's not our referendum," Wrack, the general secretary of the FBU, told around 200 delegates to the union's annual conference in Blackpool. "The referendum is taking place because of wrangling amongst the Tories. It's a result of pressure from the right-wing of the Conservative Party and the threat from Ukip."

He added: "The outcome of a Brexit vote is likely to lead to a change in prime minister, and we could end up replacing one Old Etonian for another."

"[Johnson] is the man who forced through the worst cuts in the history of the fire service, anywhere in the country, ever... So far the referendum debate has largely been a feud between elites over the best way to exploit workers."

The comments come after the Trades Union Congress, Unite, Unison, the GMB and other major unions backed a Remain vote at the 23 June ballot. The FBU recently voted to re-affiliate with Labour after Jeremy Corbyn's shock leadership election victory in September 2015.

In contrast, transport union Aslef, another Labour affiliate, is backing a Leave vote at the referendum alongside the RMT and the Bakers' Union. Will Straw, the executive director of Britain Stronger In Europe, welcomed the FBU's support for Remain.

"Being part of the Single Market, our home market of 500 million people, means more jobs, lower prices and more financial security for British workers," Straw said.

"EU law protects crucial rights at work, including entitlements to paid holiday of at least four weeks a year, maximum working hours, anti-discrimination laws and statutory paid maternity and paternity leave."

Fire Brigades Union protest
FBU chief Mack Wrack attacks the motives of the former Mayor of London Getty Images