Do yourselves this favor, it could save your life: IF you are IN a building when an earthquake hits, DO NOT IMMEDIATELY RUN OUTSIDE LIKE AN IDIOT. Your biggest chance of getting hurt is by falling brickwork when the quake is going on. Ditto, if you are outside, STAY OUTSIDE, and away from power lines. Wait until it stops and then wait a bit more before moving out if you are in or vice versa. If you really feel the need to take cover: Go stand in an *INTERIOR* doorframe, the level of support is better there structurally.
The quake you folks had could even be a foreshock to an even bigger shock. In my own experience, (besides little earthquakes that go virtually unnoticed all the time) the "big one" hit followed by smaller ones over the next week or two....but in theory that's not always the case.
If your house is shaking like hell feel free to dive under a table. And as with any emergency pre-preparations, it's never a bad idea to have flashlights, batteries, bottled water and tinned food, TP - and those space blankets are great just in case. If a REALLY big one hit, the government can't necessarily get to everyone at once. Around here a 5.1 is certainly an "attention getter" but not so much of a big deal, simply because of the construction codes. (For instance a 5.5 here would still be classed as "moderate.")
(Some of us still get excited about quakes, but for a different reason.)
Oh, and in your cases, I'd stay THE HELL out of Westminster Cathedral for a while if I could help it. Now you have a built in excuse for not going.
Stay safe, and I hope everyone is okay.