Union leaders have attacked the government for not backing new European rights for agency workers.

A report released by the TUC on Friday claimed arguments deployed by ministers and business lobbyists against new employment rules were "at worst far-fetched and at best unproven".

It found temporary work has fallen as a share of the workforce back to 1980s levels at 6.2 per cent.

The TUC also claimed nearly half of temporary workers are on fixed-term contracts, with pay and rights equal to permanent staff.

The survey concluded that in European countries where agency workers had better rights, companies had not been put off from using them.

Unions also attacked the common practice of agencies charging employers a fee for making "temps" permanent for locking workers into a constant cycle of low paid jobs rather than acting as a stepping-stone.

TUC leader Brendan Barber claimed the moral case for treating temporary workers fairly was obvious.

"It should require overwhelming evidence to persuade the government to oppose proper protection. Yet the arguments made by the employment agencies and business lobbyists do not stand up to scrutiny," he said.

"The government should drop its objections to the EU directive now that business arguments have been shown to be the prejudices of vested interests, rather than objective fact."