M&M, here's letter i'm using edit to your liking, may save your fingers and keyboard 

Make sure your full name is on letter as customer phoned me from bank as needed my last name for banks reference.
Custie can also set up themselves at home on pc.
Good luck mate.
Sent a couple more letters out today.
I do change standing order date tbh they won't all be the same but adjust standing order date so money goes into my account before their clean or not if the case be 

Will lose some but past caring now rather get around my decent custies a bit quicker than waste time on the messers.
From : Lee Dewing,  your window cleaner.
Dear Customer,
Just to inform you as from  2013,  I am changing over to Standing Order, for payments.
There is also a price increase of £1
To clean the windows of your property next time will be £6  .
I call on a 5 week basis, so 10 cleans a year.
So could you please set up a standing order for my services of  £5 a month.   
(cost of 10 cleans = £60 divided by 12 months; therefore standing order = £5).
My  Bank Account, Sort Code: ****   Account No: *******.
Please could you set up the standing order for  the date :  January 28th 2013.        
and continuing for the  28th  every month.
(I have chosen this date for all my customers so it is easy to check everyone online
at once, sorry but I can not alter the date.)
Please   email me conformation of doing this:   dcs*********.com
I hope you continue with my service but if I do not receive an email or text confirming set up of your standing order Before  January  28th  2013  then I will take this as cancellation of my services. 
If you have an outstanding balance, then please pay by internet transfer to my bank using my account details listed above. 
Many thanks,  Lee Dewing, your window cleaner.
***your address email mobile etc