MI6, most certainly, as she's stopped when driving towards the MI6 building, coming from the direction of the MI5 building.
Very interesting. Naturally, they mean MI6 rather than MI5, but I'm still intrigued by the fact that the authorities obviously appear to be aware of the attack before it happens but are unable to stop it.
I suppose it depends; they can see MI5 from the bridge.
But it is more likely to be MI6; I suppose the synopsis mentioned MI6 under attack.
To be fair; if the MI5 building blew up and you're the boss of MI6, you'd probably stop and have a look no matter which way you're driving!
But I don't doubt it is the SIS building which is under attack.