For what it's worth both First Active and Vodafone did returns of capital to shareholders in the relatively recent past so the way that they did it might have some relevance here. You should be able to Google some info about these schemes here on AAM or elsewhere on the web. On the other hand in such circumstances the company/registrar nornally issues shareholders with some summary information about the different options available and the possible tax implications of each for individuals.
As far as I recall the options of taking a capital repayment through the issue of special shares versus taking a special dividend differ mainly in terms of the tax treatment - e.g. CGT in the former case and income tax in the latter. Depending on one's specific circumstances one may be more tax effective than the other. You might need professional advice.