Calculating cost base for sale of foreign shares

Hello, I have some shares in an Australian listed company that I'm looking to sell, and have a few questions about reporting capital gains. 1. Do I calculate cost base on a first-in-first-out basis for shares? I've had a dividend reinvestment plan for a while so have acquired shares over a number of years. E.g. If I have 750 shares now and sell 400, do I calculate the cost base on the first 400 shares I acquired? 2. Do I calculate the value of shares (when acquired and sold) on the close price on the relevant dates, or the adjusted close price? 3. In my tax return when declaring capital gains, do I use the exchange rate (AUD > GBP) on the date of sale or the official HMRC monthly exchange rate? 4. According to the UK/Australia double taxation treaty article 13.5, as long as I am now a resident of the UK and no longer a resident of Australia, I can declare capital gains for the sale of Australian shares and pay tax in the UK only, and I don't need to declare capital gains from sale of shares in Australia... am I interpreting that correctly? Thanks!

Hi
Have a look at Shares and Capital Gains Tax (Self Assessment helpsheet HS284) regarding pooling shares of the same type together under a section 104 holding.
For capital gains purposes there is no fixed rate you must use.
Under the terms of Self Assessment, we do not provide an official exchange rate and the onus is on the individual to use a just and reasonable exchange rate for each acquisition and disposal.
HMRC does have a set of exchange rates for other purposes, that you can choose or you could use the closing value of the shares at acquisition and disposal.
The choice is yours.
The exchange rates provided by HMRC, can be found at Exchange rates from HMRC in CSV and XML format
and for older exchange rates at HM Revenue & Customs: Exchange rates
If you are UK resident at the time of the disposal of the share, then under the DTA, they will be taxable in the UK.
Thank you