It can happen sometimes that when you are an employer, you have not actually made any wage or salary payments for a PAYE month such as the month from 6 April to 5 May 2018. In that case you must submit electronically an Employer Payment Summary as a NIL return by 19 May. This is too easy to overlook.
If you engage a local accountant and business advisor or a payroll bureau to do your wages, then this will be taken care of. In our case we keep a diary and do a batch of payrolls at about the same time each month. Our payroll files are bright yellow like the old P30BC booklet so we do not overlook them.