Hi
Please refer to
CG73550 which clarifies what is a ‘Residential’ gain.
Where the land consisted or included a residential dwelling (which this did/does) then it is classed as residential and would be taxed accordingly.
Land that at any time is, or is intended to be, occupied or enjoyed with a dwelling as garden or grounds is taken to be part of that dwelling and so would also be subject to the residential rate on CGT.
Thank you