For the 2016 reporting period, cash taxes paid was recorded at $412 million, not the $1.43 billion you noted above. Given that, their effective cash tax rate was 10.6%, not the 36.7% you quoted.
Source: Page 22, AMZN 2016 10-K (https://www.sec.gov/Archives/edgar/data/1018724/000101872417...)
What you're missing is that the UK has been going through years of austerity. The UK public know some large companies have weird dodgy tax arrangements, and while there's some acceptance that no-one pays the real tax rate there's growing unrest about the very low rates paid by eg Starbucks or Google or Amazon.
These companies can chose to pay a bit more tax, or face tighter regulation.
The current EU VAT laws are proof the EU is happy to make onerous laws about tax
2016 pre-tax income: $3.89 billion
2016 income tax: $1.43 billion
2016 income tax rate: 36.7%
That's one of the highest rates on earth.
2015: $1.57b pre-tax income. $950m income taxes. That's a 60% rate.
They don't generate much taxable income. What exactly are they supposed to be paying substantial taxes on other than that?
Should they be paying £30m (£50m?) in taxes on that £19.5 billion in European revenue instead? Ok, let's go with that, they're both meaningless figures. How is that a substantial matter to nail Amazon for (of all things) given the epic scale of tax schemes throughout Europe?