Loan sharks are biting deeper than ever into Britain’s poorest, prompting the TUC to demand co-ordinated action on fairer pay and better working conditions.

A new survey has found that breadline workers, many on zero-hours contracts, are borrowing more and more from predatory payday loan firms.

In response unions have agreed to collective measures that include demanding better pay in both the public and private sector, as well as calling for an end to exploitative working conditions.

Unite has declared war on Wonga after research found that 12 per cent of its workers are having to resort to high street lenders to borrow an average of £660 per month.

The amount has more than tripled from an average of £200 in March 2012 and the union’s general secretary Len McCluskey condemned the figures.

“It is a tragic consequence of this government’s economic policy that those with the least are shouldering the biggest debt burden,” he said.

“The government must address the real cause of financial need — falling incomes. Low wages and insecure employment are forcing people to turn to payday lenders with their outrageous interest rates.”

Mr McCluskey also attacked the government’s relationship with Wonga, whose adverts depict human puppets overjoyed at taking out a loan with an APR of 5,000 per cent.He questioned the coalition’s contacts with other high-interest lenders keen to prey on the vulnerable.

He added: “Ministers are far too close to this industry — with Wonga founder Adrian Beecroft ensconced as a government adviser — and will not lift a finger to stop it profiting from people’s every­day hardship.”

Unison general secretary Dave Prentis also slammed Wonga at the TUC over its vulture capitalism.

He said: “Wonga’s profits up a third in a year. Borrowers — our people — desperate for a bit of cash to tide them over. Left harrowed by debt. But life is good for the super-rich.

“There has been a recovery for the millionaires — not the millions. Our people have suffered enough. We have to put an end to it.”

Augmenting the challenge, Chartered Society of Physiotherapy delegate Julia Prince demanded research into mental health problems such as stress, anxiety and depression that result from casual employment contracts in both the public and private sectors.