Thank you for your question..
The plot was integral part of the main residence and would therefor qualify for private residence relief.
The plot was sold within 18 months of moving out.. You would declare the gain from sale of land on supplementary pages SA108 - Capital Gains summary . and explain whey CGT is not payable in "any other information box".
More information on this can be found under "garden and grounds" here
I hope this is helpful and answers your question.
If you have any other questions, please ask me before you rate my service – I’ll be happy to respond.