Some of the questions in the header may now be irrelevant or have different answers.
I did get a reply from the Inland Revenue:
"The purchase date will be the OTC purchase date" (i.e. the shares bought on the OTC are the same shares sold on AIM for CGT calculation purposes)
"If the prospectus covering the purchase and sale of shares does not explain how to apportion the costs, then I assume the Revenue will accept an apportionment on a just and reasonable basis" (in response to a question about how much of the unit purchase price to apply to the shares and how much to the warrants. Did anyone work out a definitive answer for this or are people attributing all the cost to the shares and nothing to the warrants?)
"I am afraid that I cannot say whether the exercise of the warrants and purchase of shares in an open offer counts as a share re-organisation. This would not be a decision made at local office level, as it would be appropraite to the company tax district" (This was a complicated one and my memory is getting hazy. I think it was to do with either an extension of any EIS qualification - see below - or to the perceived purchase date upon exercise of warrants.)
Did we ever get a definitive answer to the EIS question? I am assuming that it is a No but do not think that has been confirmed.