To have a helicopter crash so near the site of the new American Embassy and the headquarters of MI6 raises obvious concerns for national security. I was on a train when I first heard the news, and my fellow commuters all hit their mobiles. Everyone’s first reaction seemed to be to ask if this was another terrorist attack.

It wasn’t. But for a lot of Londoners, the incident will have been a reminder of how vulnerable the capital city still is. We choose to have the headquarters of our spies in one of the most visible locations in the country. In Prime Minister’s Questions, we put the entire British government under the same roof at the same time each week — making us about the only country in the world to do this. What prevents someone renting a helicopter and doing their worst? Or renting a boat and launching an attack from the Thames?

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