Tube strike
The RMT is probably best known for its disputes with London Underground management Getty

The UK's top Eurosceptic trade union has ruled out joining one of the main campaigns hoping to secure a Brexit at the EU referendum, IBTimes UK has learned. The Rail, Maritime and Transport Workers (RMT) Union, which has more than 82,000 members, voted to campaign for a breakaway from Brussels in June.

General Secretary Mick Cash at the time blasted the political and economic union and claimed the 28-nation bloc was "at odds with the aspirations" of his organisation. Since the left-winger's Newcastle speech, Vote Leave and Leave.EU have emerged as the two organisations vying to secure the official Brexit campaign nomination from the Electoral Commission.

Support from the RMT could bolster their case by giving either group more left-wing support. But the militant union, probably best known for its disputes with London Underground management, will not be backing either campaign.

"RMT policy is to work with other trade unionists and socialists in opposing the EU and supporting British exit," a spokesman for the union told IBTimes UK.

The development comes after Arron Banks, the founder of Leave.EU, claimed that the rival Vote Leave campaign may turn Eurosceptic left-wingers off because the lobbying supremo running the group, Matthew Elliot, founded the right-wing Taxpayers' Alliance. On top of that, Vote Leave's campaign director, Dominic Cummings, is a former special adviser to the Justice Secretary Michael Gove.

But Vote Leave have been able to attract Labour MPs Kate Hoey, Graham Stringer and Kelvin Hopkins to their cause ahead of the referendum, which will be held sometime in 2016 or 2017. The group also boasts the support of businessman John Mills, Labour's top individual donor.

As for Banks, the insurance entrepreneur is a Ukip donor and an ally of the party's leader Nigel Farage. But the Eurosceptic did claim to IBTimes UK that 20% of Leave EU's 250,000 supporters are Labour voters.

"We appeal to the masses. If you look at the way we have set about doing things, we have got 175,000 followers on Facebook and we are trying to reach out to the general public with quite specific techniques," he said in October.