Whilst we can quite understand why you would want to, unfortunately it's not an option that we have available. Come to think of it, I am not sure that I have ever seen it in an online checkout. My guess is that the banks don't really want you to have that option...
If you are concerned about keeping your transaction costs down, but want an online solution, then have a look at our online Direct Debit solution. It's a lot cheaper than Paypal or Credit Cards. Click here for details on how it works, and here for a comparison on transaction charges.