I've just sent off an email to CMB to clarify pricing on their site. I noticed that the parts I was after all listed that vat was included in the price shown. However on going to the checkout page the price per item was shown as per the item page ie, the part was £5 including vat. But then lower down after postage was added, they then added on vat a second time!
I have cancelled the order until I get a reply from them regarding this anomaly. I have to say I have always had exemplary service from them and hope this is a blip in the system rather than a deliberate act.