Protest March in Argyle Street

I was going to cross the road when I saw a Protest March going along the opposite Pavement.
I couldn't figure out what they were protesting about until I saw a banner about Anti Vax. 
After a short while I thought it would be a good photo opportunity I took one photo and was poised to take another when  I felt a tap on my shoulder as I was in front of three Police Vans who were wanting to move off.  I did feel embarrassed