Temps that take on a series of long-term assignments risk damaging their career prospects and exclusion from permanent employment.

This is the warning of the Trades Union Congress (TUC) that reveals that just over half of agency workers (54%) are in continuous posts for over six months, and more than a quarter (28.4%) for more than a year.

Many temp bosses fail to see the value in training their temporary staff, resulting in a weaker position for those wanting to make the jump to better paid and more secure work, says the TUC.

With temps tending to be young people, women and older workers, the TUC warns there is a further danger that whole sectors of the workforce are being excluded from training.

TUC general secretary Brendan Barber said: "Employers aren't bothering to train agency temps who they view as 'here today and possibly gone tomorrow' and not people who are really part of their organisations. Many employers and employment agencies deny that it is their responsibility to offer training to agency workers - so temps in long-term assignments are missing out, and finding themselves ill-equipped for the future."

According to the TUC, the only solution is to sign up to the EU Directive, which would give agency workers new rights to equal treatment from the first day they are taken on.

"Day one rights would also avoid the danger that rogue employers would get round the law by taking on temps for one day short of the qualifying period. Agency workers are already facing job insecurity, and any qualifying period will only make this worse," said Barber.