This situation could be made slightly woolly by the variation in the rules relating to how they sell.
If you're a retailer, you have to price including VAT. If you sell to business, you don't have to price with VAT, although it will be charged at the checkout. If you sell to consumers and to business you can quote a VAT exclusive price, and a VAT included price.
If Google is not policing its own rules, what hope is there that sellers will follow the rules.
I would have thought that a suitable kick in the rear might be possible by reporting it to the UK VAT man. Of course, Google's UK operations relate to Ireland, however, you're talking about the UK. I would have thought that EU laws should apply.
Obviously, google's own policies should comply, too.