Normally I would pro rata pay for a leaver based on 260 days. So a client had a staff member leave at the end of June which is 65 days working days into the year. so 65/260 is 1 quarter, whcih accords with the 3 months of 12 they have worked. So you would expect that they should have been paid 1 quarter of their annual pay.
However the year 1st April 2019 to 31st March 2020 there are 262 working days (assuming monday-friday work pattern)
so the staff member hasn't quite worked 1 quarter of the year the have only worked 65/262 days. In all probability the employer will just want to pay the higher amount to the staff member but I wondered if this is actually a thing and in fact you *should* always use the actual working days in a year - or just remain consistent at 260 knowing that sometimes, yes theoretically the haven't worked the full quarter but best to favour the employee