Just a small nit-pick: in the UK tax AVOIDANCE is legal although one now has to declare any such shemes of which one is making use; presumably so that our legislature, who are incapable of writing watertight bills, have a heads up from the less cerebrally challenged.
OTOH, tax EVASION is illegal.
Basil - worked overseas, used accountant, told truth and still got a couple of years (legally) UK tax free. Even those where I had to pay had foreign tax taken into account.
I had previously run a very small business and did not use an accountant. Despite telling the truth, I ended up with the Collector's heavies knocking on the door. All eventually sorted out but it was a hassle.
HMRC will not take a private individual as seriously as they will an accountant; bit like the legal profession only really respond seriously to another lawyer.