Which countries do you think Google should pay tax in? It is accessible in almost all countries of the world - are you expecting it to pay taxes in all of them?
Suppose an American family reads the Marple website, clicks on one of the advertisers and orders some of their goods by post (you never know!). Should the Marple website pay American taxes? That would be ludicrous.
I expect Google to pay taxes in whichever country it has a physical (not virtual) presence. I'm guessing that most of its manpower and servers are located in America and will be depending on American infrastructure. Therefore, it should be paying American not British taxes.