The government is breaking the law by not forcing employers to give their staff rest breaks between shifts, the European Court of Justice has ruled.
Staff should have at least 11 hour breaks between shifts
The European Commission brought the case against the UK government, accusing it of breaching the Working Time Directive.
Britain allows individuals to opt out of the maximum 48-hour working week, but shift break rules still apply.
"Non-compliance" had been encouraged by the government, the court heard.
Britain is obliged to apply the daily and weekly rest break rules, allowing for at least 11 hours between ending work one day and beginning the next, plus a weekend break of at least one day plus 11 hours.
At the European Court of Justice in Luxembourg, the judges said the laws were not being applied properly.
Department of Trade and Industry (DTI) guidelines tell employers they must ensure workers "can" take their rest, the court heard said.
But the DTI advice does not force bosses to make sure employees do take the breaks.
The commission successfully argued that the wording encouraged "a practice of non-compliance".
"The (DTI) guidelines are liable to render the right of workers to daily and weekly rest periods meaningless because they do not oblige employers to ensure that workers actually take the minimum rest period, contrary to the aims of the Working Time Directive," the ruling said.