What is a P60 for?
It is the employee's proof of what they earned and what was deducted in the year. Anyone applying for a mortgage, claiming a tax refund, completing a Self Assessment return or checking they have paid the right tax will be asked for it. It is one page, and it is the one payroll document worth keeping for years.
It goes only to people still on the payroll at the end of the tax year. Someone who left in January gets a P45 at the time and no P60; their year-to-date figures went with them. Someone with two jobs at once gets a P60 from each employer, each covering only that job.
Like the P45, it is not something anyone types up. Payroll software totals the year's payslips, and once the final submission for the year has been made the P60 is produced from those totals. The deadline for handing it over is 31 May following the tax year end, which has been the rule for as long as most payroll clerks can remember.