I think the problem is that we have no real way of knowing how many threats have been successfully countered by the security services, and no one knows how many

I think the problem is that we have no real way of knowing how many threats have been successfully countered by the security services, and no one knows how many potential bad actors have been dissuaded by them either. So it's easy to call them out as security theatre. People on this thread are talking about the rings of steel like there’s some sort of TSA checkpoint on every road into Greater London. Unfortunately the reality is a lot less exciting. It only surrounds the square mile (a much, much smaller and higher risk area) and is pretty uninteresting. It consists of some ram-raid bollards and police booths that have fallen into a pretty bad state of disrepair. I struggle to see the downside of ram-raid barriers in a pedestrianised area - you’ll note none of the van attacks occurred in the City.