It's a non-issue if it's properly labelled as privately owned public space. It should be also clearly delimited from public space.
> Only if you refuse to leave do you commit an offence under English law.
And even that's only a civil, not criminal, offence.
I'm not a fan of Livingstone, but this is pretty good: https://www.youtube.com/watch?v=9TuxOUGV6hE
Why is that such an issue though? In the worst case, someone tells you it's private property and asks you to leave. Only if you refuse to leave do you commit an offence under English law.