If you're sat in a park with 5 others, and you know another group of 6 people who are also sat together, what is the legal guidance on how far these two groups have to be sat apart? Its certainly not illegal for people who know each other to be in the same park at the same time in different groups.
I don't think its ever really been enforceable outside in practical terms. Its, at least to my mind, there to stop LARGE gatherings (ie having 15 people in your garden MAY increase the risk of transmission, though I'd be surprised if it was by much). But when I see a group of 7 in a public space I don't really feel like they're somehow ruining it for everyone, much rather that than them meeting indoors or whatever.
If you're sat in a group of 6 and someone you know walks past are you really supposed to ignore them or tell them not to come anywhere within the vicinity to say hello for 2 minutes if you've not seen them in months. That's just not realistic. If they stand 3 metres away are they in the 'group' or not?