Joint property, 3 unequal shares - hmrc notification required?

This is a follow-on question I raised about HMRC/HMLR and unequal shares. I have it confirmed that a joint owner form is held with HMLR showing the share split. But I am confused around if/how the HRMC needs to be informed of these unequal shares for self assessment purposes. The form 17 appears to just be for married or civil partners where the ratio changes from 50/50, but our case it is me, my wife and my son who jointly own the property in unequal shares (albeit me & my wife own the same, but my son owns the majority share) and it is not clear which form should be used to notify the HMRC or indeed if there is any need to inform the HMRC?

Hi,

As it is owned by yourself, your wife and your son, you will need to write to HMRC at:

Self Assessment,
HMRC,
BX9 1AS

You will need to enclose a valid declaration of trust or TR1 land registry form showing the beneficial split. You can see guidance here:

TSEM9520 - Ownership and income tax: express trusts - written declaration

Thank you.