Hi Ben,
James is absolutely right on this, you need to take professional advice.
CGT is generally due on the Selling (contract Price) - PP - Costs of Capital/Acquisition/Sale
To do anything different will likely trigger an investigation which you will need to be prepared for.
CGT on BTL portfolios is a significant issue.
Will you be realising a profit from the portfolio?
If not, you could consider exchanging with a delayed completion (years), with a contract clause that the buyer makes and manages the mortgage payments as well as the properties.
You can sign TR1 etc so that you never have to deal with the properties again. We are currently acquiring portfolios in this manner.
Bear in mind, whatever you decide, that Exchange of Contracts is the Taxable Event, not completion. It is this date that any CGT is due from.
Phil Martin
On a Mission to Stop Repossession www.MortgageRescueNetwork.com
SARB "An ideal Answer" in print http://propertyclub.telegraph.co.uk/Page/View/282/1