Hi Thanks for your question
You are liable to HMRC for your share of the gain IF your name was still on the property when sold. (But it would be HMRC looking for this - not through your ex wife) and this is what you seem to suggest has happened - sold whilst still in joint names ? If so then yes, I am afraid you must declare your half share of the gain - and will be liable to tax on said half share.
However if the property had been transferred back to your ex wifes' sole name prior to sale, then the gain is entirely hers, as HMRC would only be looking at her to charge the gain on.
Thanks for your response.
My name was never on the register of title at the land registry. The 50/50 split was done only via a declaration of trust, which I assume HMRC would never know about unless I refused to pay and my ex-wife gave it to them?
I was hoping that as I never 'gained' from the sale I wouldn't be liable.