I find it hard to accept that the HMRC are struggling that hard to get their paws on what Starbucks et al should have paid. As noted elsewhere they are much happier hounding the little guy who cannot afford a high end tax lawyer.
Twenty years ago I was working in France on a campsite for the equivalent of about £85 per week. I was paid in cash but my employers reassured me that they took care of the tax side of things with the French.
Sadly when a year later I had to complete at Tax return the HMRC took a very different view and enthusiastically pursued me for their share of my massive earnings. Ok, fairs fair and I should have looked a bit more closely at my employers advice. However if pound for pound the HMRC invested the same effort in pursuing Amazon as they did for my meagre offer their tax bill would not be an issue today.
What I see is a cosy relationship with big business. Take the money off us poor sods on PAYE, hound the self employed builder and cheerfully ignore the big fish funnelling their profits through tax havens. Why? Because they have the money to fight and the friends in high places.