The European Court has ruled that employers must keep records which record “objectively and reliably either the number of hours worked by the worker [or] when that work was done.”
This UK’s Working Time Regulations do not currently impose such a requirement so, subject to Brexit of course, the government will need to amend those regulations.
In practice for most employees who work regular hours and under 48 per week an issue is most unlikely to arise. However, for travelling or homeworkers and others who may work longer or less predictable hours which are difficult to evidence, then prudent advice is that steps should be taken to report and maintain a record.
That said, this ruling probably creates more red tape and administration for businesses where problems haven’t arisen previously and are unlikely to arise. Most workers and businesses have managed just fine, thank you very much. Even before this decision, prudent advice would have been exactly the same since someone could complain their hours breached the Working Time Regulations and any dispute would best be resolved by examining records of their hours of work.