The government will require a 14 day quarantine period for air travel passengers arriving in the UK. This is going to be at a private residence. What is to stop people agreeing to this and then going their own way?
My dh had a 14 day compulsory quarantine when he returned to China, but this was in a designated facility. Prior to this people were allowed to self quarantine in own homes, but you were visited every day to ensure compliance.