Yep, it is. I can attest to that from first hand knowledge. I was visiting London a few months ago and was doing some night time photography of The House of Parliament and Big Ben from across the river, not far from the London Eye when I was approached by two police officers. They questioned me and were very interested in what I was photographing. They were polite, but there was no doubt in my mind that I was being treated as a suspect. I was informed that I drew their attention because I was using a tripod. They said I had to give them my identification so they could check me out. They radioed my information into dispatch and after a few minutes I was cleared (not a terrorist). They wrote out an incident report, gave me a copy, and told me to show it if I was stopped by police again while taking photos and it would show that I had already be investigated and cleared.
Since I was a visitor in a foreign country I was very cooperative. I did politely ask them why I was singled out for investigation while there were several other people taking photos in the same area. They said it was because I was using a tripod which would result in sharper photos (this was night time). I wanted so bad to challenge them about why they did not investigate everyone photographing the same location during the daylight hours - after all it wouldn't be much different than night time with tripod. I was so tempting to speak my mind, argue my rights, etc., but I knew there was nothing to be gained by being confrontational with police officers.