Admittedly, Google are late to roll out Google Wallet to the UK, but your experience is nothing like that of which Android is capable in the US.
I tap my phone and get a pin dialogue box. Enter my pin and confirm the payment. I can change which credit card I'm using if so desired.
The process is as seamless as you can really expect from a user point of view.
The problem for me is that I'm billed by Google rather than the store, and this limits my cash back substantially. That, however isn't Google's fault - the banks didn't want to play ball and instead wanted convoluted systems like the one you described.