The £30,000 bung will only be an attractive option for the super-rich who would have to pay more than this in UK tax if they disclosed their world wide income.
What seems to be often overlooked is that UK tax will only be payable over and above any local taxes payable on offshore income and gains. Thus if the local taxes are 25% only a further 15% UK income tax would be payable here. If of course the income or gains are not being taxed overseas then the UK tax bill could be as high as 40%.
What levels of taxable income would warrant the payment of the £30,000 bung in preference to 40% tax? Well - An investment of £1.5 million generating a not very exciting return of 5% would yield £75,000. 40% of this = £30,000.
Remember too that if a taxpayer elects to pay the £30,000 this will mean that they will forgo their entitlement to a personal allowance and to the CGT annual allowance. These will no longer be available to anyone who wants to be taxed on the remittance basis (and who pays the £30,000 as a penalty for so electing).