Although the USA has a much-more overt (and continuous) Homeland Security / Disaster Preparedness agenda, the UK and all other European countries have been doing this (usually on a low-key basis) for many years.
I suspect that (in addition to there being a UK Central Goverment core initiative to this-
#30Days30WaysUK is the social media hashtag) there is something of a neocontemporary internet-amplified echochamber going on, which is being fuelled by some rather ill-advised cut-&-pasting of North American personal security advice into a UK context.
Just imagine how fevered the Millennium Bug non-event
would've been, if December 1999 had been possessed of the level of internet interaction we see now in September 2019.
And as for the realities of 'grab-bags'....I don't carry as much (on my person, or in my car) as I used to, but it utterly-astounds me that vast numbers of Brits wander out of their houses in teeshirts and jogging pants, jump into cars with empty fuel-tanks and crash into ditches, in the sure & certain expectation that agents of the local authority and the government will magically-appear to save them, the minute they make an emergency call on their uncharged phones.
I recently had an accidental conversation with an early middle-aged lady at the bus-stop, wherein the topics of unexpected power-cuts and fuel supply difficulties were being discussed with a young (but impractically-tall) boy. She was assuring him that "these days those sorts of things just don't happen any more".
I think her attitude reflects that held by many of The Great British Public, in that now we have 24hr Tesco supermarkets and McDonalds, and cars that can just be plugged-in anywhere, there will >never< be challenges or changes to the ambient utopia we all bask in the warmth of.
Being older of age, longer of tooth, and shorter of faith, I remain calm: because everything we hear or can be told is merely a perspective and a narrative.
But I am always a little prepared for everything. And anything.
Otherwise I would not consider myself to be a human....
“A human being should be able to change a diaper, plan an invasion, butcher a hog, conn a ship, design a building, write a sonnet, balance accounts, build a wall, set a bone, comfort the dying, take orders, give orders, cooperate, act alone, solve equations, analyze a new problem, pitch manure, program a computer, cook a tasty meal, fight efficiently, die gallantly. Specialization is for insects.”
― Robert A. Heinlein
I guess it's because somebody decided to make September 'preparedness month'
I'll go with since Sept 2014, on that one. But it has a much (much) older pedigree than that...late 1960s, really.