What rate of the national minimum wage is payable when 1 April 2020 falls within a worker's pay reference period?

Regulation 4B of the National Minimum Wage Regulations 2015 (SI 2015/621) states that the hourly rate at which a worker is entitled to be remunerated in respect of any pay reference period is the one that applies to the worker on the first day of that period. This means that where a pay reference period began before 1 April 2020, the old rate of the national minimum wage will be the one to which the worker is entitled for that reference period.