Standing orders were a preferred method as the set-up was passed over to the client, but complications arose as and when it was necessary to revise the amount of payments due.
For firms that charge fees on a fixed or variable basis, and that are discomforted by the delay in their present collection processes, can I suggest that they take a look at the online service GoCardless. It is a much more accessible method to collect payments than the alternatives offered by the major clearing banks.
I use GoCardless to collect recurring and non-recurring fees from customers and can heartily recommend the service. Set-up is straight-forward as is day to day admin.
Getting approval from clients to use direct debit is another challenge. A strategy that seems to work is to offer a discount for DD settlement. The service is cloud based so your clients will need to go online to provide their permission for the process.
If you are concerned by the level of your debtors, this might be a solution.