Since 6 April 2020 if you are a UK resident and you sell a residential property in the UK you have 30 days to tell HMRC and to pay any CGT owed, save for exceptions such as where Private Residence Relief applies. Otherwise you may be sent a penalty as well as having to pay interest on the tax owed.
Non UK residents still have to report sales or disposals of interests in UK property or land (whether or not there is a CGT liability) within 30 days of completion of the disposal but tax may no longer be deferred via Self Assessment and any tax owed must be paid within the 30 day window. This includes disposals of residential properties, non-residential properties and indirect disposals.
Reporting is now through the Government Gateway online service and sellers should note that it can take some time to be registered for the system and/or to authorise an agent to carry out this reporting. This is particularly important for trustees selling trust property who may need to obtain a Unique Taxpayer Reference for the first time before accounting for CGT.
The 30 day deadline is now back in force, having been temporarily waived during the COVID-19 lockdown.