SJ, although I would allow for differences between how e-bay works in the U.K., vs how it works here in the U.S., I found, sometime ago, if you set up your preferences to do so, it's much simpler to let e-bay take care of the no-pay customers we all experience from time to time.
In my case, ff the sale languishes in the "Sold" bracket for over 5 days, e-bay contacts the buyer and if the payment isn't forthcoming in 7 days, the sale is cancelled, you get the seller's fee credited back and the buyer has a black mark in their feedback.
You can do the same thing by going to the 'Resolution Center' and opening a case there. You wouldn't have to wait the 5 days in that situation.
In either case, I would send a friendly sounding reminder to the buyer that you can't ship the item until payment is received… e-bay uses that as good faith on your part in an attempt to resolve the issue...