Define reasonable? It's already been decided it's legal and not tax evasion, and doing something illegal.
I define it the same way that the legal profession does. Put it to a jury. Let them decide whether the tax-return is a valid representation of the company's tax affairs, or whether they are fabricated financial structures designed to avoid the paying of taxes that parliament and the treasury intended and expect companies to pay.
If we decide whether someone goes to jail by presenting the jury with evidence and them deciding if a law was broken, why can't we do the same with CFOs and blatantly tax-evading tax returns?