Speaking at the GMB annual conference in Brighton this morning (6 June) Cable warned that co-ordinated strike action would lead to tougher union laws.

There has been a call from Conservative party members, including London mayor Boris Johnson, to raise the level of support required for walkouts, with a proposal that at least 40% of the balloted workforce must vote, as well as a majority favouring strike action. Currently there is no minimum response required.

Sibbald told PrintWeek that any changes to the law would be unlikely to affect print, where 90% of balloters would often respond.

However, he blasted the government for simply following "Tory dogma" and attacking the union for no reason.

He said: "They think to themselves 'we are the Tory party, we have to attack the union, that’s how we win votes'.

"The UK has the lowest number of days lost to strikes in Europe and when we go about seeking action we do the same thing that every other democratic organisation does in the world, we set out options and then our members go to ballot.

"It is exactly the same as voting in a parish election or a national election, it is a pretty rich claim coming from a party that are in power despite only being voted for by about 25% of the population.

"These government cuts will affect the working people, Boris Johnson won't be affected by them. We are the only organisations speaking out for the working people, the people affected by what is going on and we are getting attacked by the government for that out of nowhere."

Sibbald's opinion is obviously shared by many of his fellow union members as Cable was heckled while giving his speech this morning.

The threat was made ahead of a proposed walkout of 750,000 public sector workers on 30 June.

Sibbald said that often public sector votes for industrial action did yield poor response rates. A civil service strike in June yielded just 30%, while tube strikes last June saw just 38% of balloted members vote.