Hello and welcome to the site. Thank you for your question.I am sorry to say there is no extra CGT relief for investments held for longer period.Capital gain is based on the difference between cost price and net sale proceeds irrespective of timescale. Indexation allowance came to an end in 1993.
CGT simplification came into being for all disposals on or after 6 Apr 2008.More information on indexation allowance can be found here
I hope this is helpful and answers your question.
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