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?

The answer is the ongoing work of our security services, who disrupt terror cells before they strike. Logistically, there isn’t much to stop serious terror attacks in London. When Rupert Murdoch was struck with a pie in the House of Commons, or a protester remonstrated face-to-face with Tony Blair in the Leveson Inquiry, it reminds everyone that security is far from impenetrable. We don’t run our capital city like a military base, we’re a open country and we choose not to live like we’re under siege. The low incidence of successful terrorist strikes here is not related to an ring of steel but to the incredible work that the security services do on our behalves. The mark of their success lies in what does not happen, not what does happen. The thwarting of the Heathrow Plot in 2006 was a remarkable story, which even now pretty much remains untold.

This morning’s crash was a scheduled helicopter flight from Surrey to Hertfordshire that tried to land at a Battersea heliport due to bad weather. Not many heliports have cranes so close to them. The accident claimed two lives, and as the Met say it’s miracle the death toll was not higher given that it happened at the rush hour. But it’s not a miracle that there has not been another 7/7 in London. It’s down to the hard work and professionalism of those whose job it is to disrupt the bad guys in time.

Tags: PMQs, Terrorism, UK politics