Ten trade union leaders have combined forces for a rare joint appeal to their collective membership to stay in the EU, saying Tories threaten workers’ rights in the case of a Leave vote.

Len McCluskey of Unite, the UK’s largest trade union, along with nine other union general secretaries, has said the benefits of membership far outweigh any positives from leaving in a joint letter to The Guardian.

They highlight maternity and paternity rights, equal treatment of part-time and agency workers and the right to paid leave as rights underpinned by our membership of the European Union. The group then add that Conservative figures would “negotiate away” these rights if they oversaw a Brexit.

“If Britain leaves the EU, we are in no doubt these protections would be under great threat. Despite words to the contrary from figures like Iain Duncan Smith and Michael Gove, the Tories would negotiate our exit and, we believe, would negotiate away our rights.

“We simply do not trust this government if they are presented with an unrestricted, unchecked opportunity to attack our current working rights.”

In addition to McCluskey, the letter includes signatures from Dave Prentis of Unison, Tim Roache of GMB, Manuel Cortes of TSSA, John Smith of the Musicians’ Union, Dave Ward of CWU, Matt Wrack of the FBU, John Hannett of USDAW, Gerry Morrissey of Bectu and Roy Rickhuss of Community.

The most recent YouGov poll has put Leave ahead with 45 per cent of the vote, compared with Remain’s 41 per cent.

Their letter comes at the same time as Hilary Benn and Angela Eagle launch a demand of Out campaigners that they be clear with voters which rights they would see binned if we left the bloc.