Go cardless and google checkout allows you to email folk a payment link and for then to pay in line.
You can also set up pre-authorisation on the customers account, SI you XS take variable amounts of each month in gocardless - first payment can take 7 days to process though, plus side £2 is highest commission or 1% what ever is lowest !
I use kashflow for my invoicing and it has a gocardless option on each invoice.
only using in for few weeks but like it!
SPRmarine / SPRtraining
RYA Training Courses & Safety Equipment Sales