cbjohn wrote:I'm sitting on an unrealised £20K gain with the shares.
Do you mean that you are sitting on this unrealised gain or that your company is sitting on this unrealised gain?
cbjohn wrote:I'm wondering whether I now need to pay the higher rate of tax.
You haven't referred to you having any profits/income, only that your company has.
Hence you need to differentiate between you and your company.