Dircet debits (Where your bank requests payment from your customer) are the subject of the "direct debit guarantee" and are only available to companies with turnover greater than £500,000
You could however ask your customers to pay by standing order, whereby the money is sent from their account to yours every month on a set date. I have heard of one customer who pays this way, and it seemed to work fine. If you miss a month because of bad weather or illness, simply pop a cheque through the door to even things up again.
Silly