Base price for CGT calculation

[GW]

Hi, I'm confused by HMRC's documentaion re calculation of the base price, prior to a proposed bed & ISA share transaction.

Briefly, I acquired Standard Life shares on 10th July 2006 (free shares acquired as a member of SL prior to demutualisation, plus others that I purchased on the same date). I understand that for CGT purposes, these shares are "pooled" and the base price is calculated by dividing the total cost by the total no. of shares. This I have done and the average price of the pooled shares is approx. 135p.

I also acquired some free SL (bonus) shares a year later, on 10th July 2007 - obviously at zero cost.

I am considering moving some (or possibly all) of these shares into an ISA (bed & ISA), which allows the shares to be repurchased immediately, but will give rise to a potential CGT charge (I'm aware of the current CGT allowance but, as I have other capital gains, I do not want to exceed the annual allowance).

I now need to calculate my CGT liability prior to moving (some or all of) them into an ISA in the next couple of months.

Any advice on how to calculate the base price for such a move would be extremely helpful. Thanks, George