Our readers will be aware the Working Time Directive is health and safety at work legislation, brought into force in NI in 1998 and now consolidated under the Working Time Regulations (Northern Ireland) 2016. The Regulations entitle workers to annual leave, daily breaks and weekly breaks, amongst other things.

In relation to weekly breaks, workers are entitled to a minimum of one day off in every seven. The question, in this case, was whether the weekly rest has to be taken at the end of six days of working, to allow for a break between weeks, or whether workers may lawfully be asked to work up to 12 days in a row, provided they are given two days' rest in every fortnight. The answer is the later, according to the CJEU:

"...Member States are to take the measures necessary to ensure that, ‘per each seven-day period’, every worker is entitled to a minimum uninterrupted rest period of 24 hours plus the 11 hours’ daily rest referred to in Article 3 of Directive 2003/88. However, that article does not specify when that minimum rest period must take place and thus gives the Member States a degree of flexibility with regard to the choice of timing.

... an interpretation of Article 5 of Directive 2003/88, according to which the minimum uninterrupted rest period of 24 hours, plus the 11 hours’ daily rest referred to in Article 3 of that directive, may be provided at any time within each seven-day period, is supported by a systemic analysis of that directive...

It is apparent, therefore, from the actual wording of Article 5 of Directive 2003/88 that it requires the Member States to ensure that every worker enjoys, during a seven day period, a minimum uninterrupted rest period of 24 hours plus the 11 hours’ daily rest referred to in Article 3 of that directive, without, however, specifying when that minimum rest period must be granted."
http://www.bailii.org/eu/cases/EUECJ/2017/C30616.html