Earlier quoted context omitted.
As I recall, to get prosecuted for tax evasion in the UK, you need to not only commit the tax evasion, but also to lie to the HMRC investigation of the tax evasion, at the point where they ask you to sign a form that explicitly says that if you lie now and they find out, they will put you in jail. So unless you lie at that point, you will not be prosecuted, only investigated. This may let some tax dodgers off the hoo…
Protecting people from their own mistakes is fine, but they lost that defence once they put the money in secret swiss bank accounts. Secret. Swiss. Bank. Accounts. Might as well accidentally ask the local mafia to white wash some money while they twirl their mustaches.
It first becomes tax evasion (in the UK anyway; details may vary) the moment you fail to report income or capital gains that are taxable, since the UK does not tax wealth.