There was an interesting discussion on BBC news the other day, the interviewee pointed out that 'exercise' was walking or jogging etc., possibly with one other person. However, the moment you sit on a bench with your companion, possibly even drinking a coffee, you aren't exercising, you are 'socialising' and it's the socialising they are wanting to stop. Sat chatting, you are more likely to spread/catch any possible virus. I could understand the thinking in that...
Someone stopping for a moment to sit down, alone, while they catch their breath, doesn't appear to be the same. But I suppose if they are sitting for a while they need to be moved on as it's no longer exercise.
I feel sad for people in London, pictures on the TV show hundreds of people still out in parks, it looks as busy as a summer's day, hardly a lockdown. With so many crowds, I can see the police need to keep folk moving.
Out here it looks like a proper lockdown, the roads are empty and on my rural walks....I think I walked 5 miles yesterday and I did see one dog walker in the distance at one point. No-one else....