When does CG become due with deed of trust?

My brother and I are joint owners (tenants in common) of the property where I live. I am buying him out of his share in instalments. We have drawn up a declaration of trust for this which specifies when the payments will be made. Will he be liable for CG on his share when the deed is signed, or when he receives the first payment? How long will he have to pay it? Thanks.

Hi Clivechaf Chafer,
Yes, he will be liable to capital gains on his share if being sold for more than he paid as it has not been his only or main residence.
Any tax due will be when the deed is signed as this is classed as the sale.
As you are paying in instalments, he can ask for deferred consideration to pay any capital gains that may be due.
Please see:
CG14881 - Deferred consideration: what is ascertainable
Thank you.