The arguement being "the Americans don't do that, so why do we?**" here is what I have to say about it:
You should be taxed even if you're working outside of the UK, why? Because you're being employed by a British organisation. If you're working on a base in Germany, well who fucking cares, you're still being paid by the same organisation, nothing is going to change that, unless that is you start working for the German government.
This is the same under the Canadian tax
Makes sense? no, probably not, because I couldn't explain taxation if my life depended on it. But whatever, I assume you get the jest of it all.
* = Who is responsible for naming these stations at the beeb? Really "Radio Five" will suffice.
** = not actual statement, but a summarised version.... in my own words.