This is kind of surprising in case of Britain. As long as I remember both Cayman islands and City of London, two of the best known tax havens, are British territories so Britain could prevent tax evasion easily.
When it comes to "taxing" those pesky Facebooks and Netflix globally, I am not sure I understand justification for this.
Companies pay taxes because they use resources and services provided in a given country (roads and other infrastructure, police protection, courts, etc.). Facebook does not use any resources in, say, Belgium, so why it should be taxed there?
If a company located in US, like Facebook, avoids paying taxes there (strange that someone who pretends to be rather left leaning person like FB owner escapes taxes, but that's a different story) it is the US problem, not a global problem and they should sort this out somehow - for instance make FB to pay directly for services/resources provided by the state, maybe in the global economy corporate tax does not make much sense any more? I can imagine that Facebook has some fake office on Caymans, but I hardly believe they would relocate there data centers and employees to avoid taxes, so making tax proportional to number of employees in the given jurisdiction, size of the office, used electricity, etc. might make sense.