Police have disabled two car bombs containing gas cylinders in the heart of central London. The BBC News website asked people working and living in London about their safety concerns after the discovery of the first vehicle.
Rami Harb, 36, doctor, from Camden
When you hear about something like this, you become more cautious about going out.
I escaped the car bombs in Lebanon to come to London but I still think this is a safe city.
We don't yet know who is behind this but the UK has become a target because of its efforts to promote democracy abroad.
Frances Leung, 29, anaesthetist, from Westminster
It's not the first time and it won't be the last. I feel safe actually. If it happens, it happens.
I don't feel they are targeting me. After the July bombings I was more concerned about reassuring my family than about my immediate safety.
Walter Wells, 69, retired academic, from Westminster
It's sad but unsurprising. I've lived here nine years. The chances of becoming a direct victim of such an attack are low.
My wife and I are city people. This is home...we won't be driven away by fear.
Clemmie Coltart, 24, assistant TV producer, from Westminster
I find it extremely shocking. I certainly don't feel as safe as I used to.
There was always a possibility of something like this happening because of the Blair-Brown handover.
I'm actually more concerned about gun violence at the moment than I am about terrorism.
Linda Nicholls, 58, legal executive, from Oxford
I feel as safe here as anywhere. I'm not surprised to hear about police finding an explosive device.
I'm a bit of a fatalist really. If my number is up, it's up. There are dangers everywhere you go.
Rhys Price, 18, carpenter, from Hayes
I was on the Tube this morning when we were told Piccadilly was closed. I got a call from my mum, who was worried.
You reach a point where you have to get on with it but the possibility of another attack is always at the back my mind.