What about TUPE?

Employees transferred under the Transfer of Undertakings (Protection of Employment), or TUPE, regulations should be paid at least the Living Wage in line with your other employees.

The licence requires that all those employees who work for you for 2 or more hours a day, in any day of the week, for 8 or more consecutive weeks must be paid the Living Wage. So technically you have up to a maximum of 8 weeks to implement the pay increase.