Do we now require voluntary taxes from candidates?

I'm no fan of Zac Goldsmith's policies, and I'm not convinced it was wise for Cameron's team to give him such prominence.  But I'm dead against Cameron's requiring of him to abandon his non-dom status.

As I understand matters, Zac Goldsmith is legally entitled to non-dom status.  Now, that may be silly, and non-dom status may have become a ridiculous scheme for those entitled to multiple passports to get a tax break, but if so then change the law.  Currently, the law is as it is, and all Zac Goldsmith has done is to organise his matters in a tax-efficient manner.  For him not to do so - for him to abandon his non-dom status - would be a quite straightforward case of his volunteering to pay extra tax.

If we think Zac Goldsmith should volunteer to pay extra tax, then we should just ask him to do so.  How much voluntary tax is a continued Conservative candidacy going for these days?  Will £0.5m or so suffice?  Or is it a percentage of his total wealth?  How about 0.25%?  How much excess tax is Mr Cameron volunteering to pay?  What's 0.25% of £30m?  Will £75,000 cover it?  How generous is William Hague feeling?

Or is the point that the Conservatives are proposing to do something about non-doms?  (In fact, as I understand it, there is no Conservative policy to change this law such that Goldsmith would no longer qualify - merely a levy on those taking advantage of it - but let's ignore that for now and assume we were going to disqualify people in his circumstances from non-dom status.)  So do Conservative candidates now have to make their current tax arrangements "compliant" with future Conservative tax plans and pay the difference in voluntary taxation?  We favour a 50p rate now.  So will anyone standing as a Conservative candidate with income above the threshold be paying 10% of their additional income in voluntary taxes?  It seems we might favour taxing debt interest so as to equalise it with dividend taxation.  So should any Conservative candidate with interest income be estimating the tax they would have paid and send off a cheque?

Obviously I am being ridiculous.  Yes.  Precisely as ridiculous as those urging Zac Goldsmith to volunteer to pay taxes that the law, as it stands, does not require him to pay.