The European Court of Justice (ECJ) ruled on Thursday (7 September) that the UK must change guidelines saying that employers "must make sure that workers can take their rest, but are not required to make sure they do take their rest."
The court said the European Commission, which had taken the country to court over the issue, was right in saying that the UK guidelines clash with the EU's working time directive which defines maximum hours for people to work.
The EU law stipulates that an adult worker is entitled to a rest period of at least 11 consecutive hours per day, as well as an uninterrupted 24-hour break a week.
The Luxembourg-based judges ruled that London's guidelines - distributed to people in order to understand the EU legislation - are "incompatible" with the working time directive as they "restrict the obligations on employers as regards the workers' right to actually benefit from the minimum rest periods."
The commission said it "welcomes" the decision, with a spokeswoman saying that "the daily rest of workers is a right and cannot be renounced."
"Employers must ensure that workers have rest periods. it is a matter of health and safety and is not something that can be traded off," she added.
'Kick in the teeth'
British conservative MEP Syed Kamall was however quick to criticise the ruling, saying "This is a kick in the teeth for British workers who may want to work longer hours to pay for extra bills or family holidays."
Stressing workers' own choice to determine their working times, Mr Kamall stated that "while many people have a healthy work-life balance, others may choose to put in extra hours to achieve their ambitions."
But Dutch socialist MEP Emine Bozkurt hailed the ECJ's judgment, arguing Mr Kamall's notion of "choice" is misleading.
"Many employees are not given any choice by their employers when they are under pressure to work longer hours. Workers who are at risk of losing their job cannot simply say: no, thank you," she stated.
Ms Bozkurt added that the ruling represents "a great step forward" in a broader political battle on the future of the working time bill, which is currently under revision.
London, backed by several "new" member states, is trying to preserve an opt-out which allows workers to agree to work longer than the 48-hour maximum per week on average, prescribed by the directive.
But states like France and Sweden have pressed for the opt-out to be scrapped, with a June ministerial meeting over the issue ending in stalemate.
On top of this, governments are divided over contracts used by more workers at the same time, with some in favour of applying the 48-hour limit to an individual worker, and others to a single contract.
The Finnish EU presidency is currently considering ways to break the stalemate, with a meeting on the issue on the cards "quite soon," according to a Finnish contact.
But Helsinki will have a hard time finding a compromise solution acceptable to both camps, with all four previous EU presidencies failing to do so.