Private residence relief with no nomination of main residence

In the scenario where there are two residences but no nomination was made as to which should be treated at the main residance, CG64545 states "Where a notice is not made, or an invalid notice is made, the residence which attracts relief is the dwelling-house which is the main residence as a matter of fact." It gives some examples of things that are relevant to considere but it seems some level of subjectivity is involved rather than there being an unambigous definiton. In this scenario, what is the recommended process for someone filing CGT when a residential property is sold? Does one agree with HMRC in advance through some process, or do you file the CGT and HMRC will respond later if they have concerns?

Hi Alex Pollitt,
You need to have this confirmed in advance to ensure the correct reliefs, where applicable, are applied.
Thank you.