I am at the moment sitting at my desk writing a letter to 5 habitual late payers... Asking for them the settle their current outstanding balance by bank transfer...
At the bottom of the letter in a larger font I have put the follwing:
----------
PLEASE NOTE: If you would like us to continue providing a regular window cleaning service please register to pay for future window cleans by direct debit.
Future payments will then be processed automatically by direct debit approximately 5 – 7 days AFTER a window clean.
Your regular window cleaning service is currently suspended pending direct debit registration.
Register online at www.iconicwindowcleaning.co.uk/directdebit
----------
It will be interesting to see if any of the 5 register.
Andy 
Hi Andy
I have been doing the same thing letter wise for about 6 months and in my experience so far most have then signed up. I have similar on the end of the payment reminder.
We ask now that if you wish us to continue providing you with our window cleaning service that you use the Direct Debit payment option as your method of payment for all future cleans. No further cleaning will take place until we receive confirmation that a Direct Debit has been set up.
To set up a Direct Debit go to
www.impactcleaning.net and click on the payments page.
Simply fill out the form on our website (takes less than 2 minutes) and that’s it, all future payments are then collected automatically by Direct Debit.
With the Direct Debit payment system we will only ever collect payment AFTER your windows have been cleaned (Approx. 3-5 days). You can cancel the Direct Debit at any time. This payment scheme is covered by the Direct Debit guarantee.