The kernel of this is likely to be the story of an English woman being arrested for silently praying outside of an abortion clinic/centre a couple of years ago. There was an exclusion zone around the clinic that banned any protest - including things like counselling people going into the clinic. From what I've found, it seems to be a law specific to Birmingham council, rather than the UK as a whole -- which strikes me as odd, I had no idea that local councils could do this. The lady in question was outside the clinic, standing quietly and being filmed IIRC. Police spoke to her, and she then confirmed that she was praying silently in her head, which was taken to be admitting to breaking the exclusion order within that location.
So while it is a horrendous abuse of free speech (which doesnt exist in the UK anyway), it was specifically limited in the context of being in a hyper local area (outside an abortion clinic) within a community (Birmingham) that had enacted this local law. Jack has spun that to mean that Christian prayer is illegal throughout the country -- a country whose monarch is literally the head of the Church of England, who are (if only nominally) fans of praying to Jesus.
