The opinion, given by three barristers - one a Queen's Counsel - has been sent to all heads of chambers. It makes it clear that all trainee barristers, known as pupils, are now subject to the 1998 EU Working Time Regulations, while those over the age of 26 qualify for the national minimum wage.
As a significant proportion of barristers' pupils are over 26, the opinion will mean that chambers must pay pupils pounds 8,000 a year. In the past they have paid them nothing. This practice, mainly restricted to smaller sets of chambers, has obliged aspiring barristers to take unfunded pupillages.
Steve Doherty, a spokesman for the Bar Council, said that those chambers that did not comply with the guidance would be "flouting the law of the land" and that the Bar Council would take a "dim view of this".
He admitted that chambers adhering to the new laws might be forced to cut the number of pupillage places available. "We simply don't know how many unfunded pupillages there are because chambers are not obliged to tell us," he said.
But it has been common practice in some chambers to take on more pupils than can be offered permanent employment, so that there are sufficient pupils to carry out support work for senior barristers. "It's really very cheap skilled labour,"said Mr Doherty.
The opinion, given by Jeremy McMullen QC, Jennifer Eady and Sarah Moor, says that under the Working Time Regulations chambers must also give pupils three weeks' paid holiday. But it also says that chambers can enter into individual written agreements with pupils to "contract out" of the 48- hour week.
David Richmond passed his Bar exams in 1992 but after several attempts at finding a funded pupillage he was forced to abandon his legal career and take a job as a waiter in the department store Harvey Nichols.
"I was paid much more as a waiter than I would have been as a pupil," said Mr Richmond. "It came to a point when I had to decide how much longer I could continue living on the breadline." Mr Richmond, now a magistrates' court clerk, says that he blames the "sweatshop" mentality of some chambers for his inability to find a pupillage. "There are dozens of talented trainee barristers without private incomes who have to sacrifice their career at the Bar because of money problems," he said.
Nigel Savage, chief executive of the College of Law, said that he welcomed the opinion because it would force chambers to pay their pupils an honest wage for an honest day's work. "If they are not prepared to do that then they shouldn't take them on in the first place," he said.
Georgina Kent, chairman of the Young Bar, said that she too welcomed the development: "It will make chambers think how they are going to award pupillages in the future."
She added that some chambers, mainly civil sets and the better-off criminal chambers, did already pay pupils the equivalent of the minimum wage during pupillage.