Employers employing more than 50 employees (including agency workers), are required to take reasonable steps to facilitate employees to take COVID-19 tests when they travel across international borders.
DHSC guidance stipulates ‘reasonable steps’ to facilitate the taking of tests might be:
• establishing workplace coronavirus (COVID-19) testing or providing employees with home testing
• supporting access and signposting employees to testing outside of the workplace.
Further (extensive) details are here.