Over 60 killed in terrorist since 7/7/2005. But of course more are killed on UK roads in a typical month so I recognise that a sense of perspective is required. However I also have some knowledge of the background and the degree of known threat against the UK on a daily basis and concerns me...
Hopefully just a precaution - and a peaceful outcome.
After the Woolwich incident it is reassuring to see some decisive action rather than let the bad guys make all of the running, which makes the country look like a soft target.