Australian share-based pension

I am helping my father in law. In the late 70s a company he worked for provided a pension in the form of shares in what is now the ‘Commonwealth Bank of Australia’. The total value of the shares now is approximately £30,000 and he has just sold them and is bringing the money back to the UK as a single transfer (as the AUS share company is very disorganised so bringing back in stages was not an option). He has no idea of the starting value of the shares as he has no payslips from back then to say when the shares were brought. Questions: Is this a capital gain, or income, or could it be treated as a pension lump sum? Do we need to work out the initial cost of the shares - if so will HMRC accept a pragmatic midpoint of employment share value x shares? What do we do if the company has revalued or changed shares since the 1970’s? He has received share statement and small dividends for years but has not considered before how the money will be taxed on return.

Hi,
It sounds like this is capital gains as actual share certificates were issued. you would need to check with the stock exchange for prices.
Thank you.