It is his right unless the pub garden has rules against it.What he said above.
I've taken a phone off someone who thought it was amusing to take a pic of me and my wife in a pub garden because he thought it was hilarious we were mucking around wearing paper hats crafted out of newspapers because it was raining.
I gave it back to him after I did factory reset on his phone.
He also thought it was his right.
The twat.
Personally, I don't think people should lose their right to privacy by leaving their home, but ultimately they do. If they didn't the press would have no right to report at all.