I work close to Parliament, and our office was put into lockdown when this happened. The street outside was rapidly cleared and armed police officers patrolled the area. We relied on the news to find out what was going on. If there had been a news blackout, people would have rapidly come up with their own explanations — conspiracy theories can easily mushroom through lack of information*.
Whilst I think the media coverage was a little overblown, there is strong circumstantial evidence that this was Islamist terrorism. Labelling something ‘Islamist’ or ‘terrorist’ (a) make a story ten times more newsworthy than it may have been otherwise and (b) plenty of people see whatever they want to see reflected in these labels. I’m more frightened by some of this social media reaction than the original news reporting.
*shortly after the 7 July bombings, explosives were found at Paddington Station. This was never reported at the time, and I only found out from a colleague. What was going on? Were things being kept from us? A couple of months later, the story was reported—the explosives belonged to the London Fire Brigade, who had forgotten to pick them up after a training practice.