I'm sure I read something recently which explains it (can't remember where exactly but it was from quite a reputable source, I think. Possibly the Economist, or somewhere like that) It looked into how this type of conspiracy theory thread comes about. From vague memory it said that whenever there is a press release about an update to public information, even though that's literally all there is to it - that there has been a change to some website or other - some bugger will jump on it and assume that BECAUSE it's reported widely in the popular press that there must be a deeper, hidden meaning and "something we're not being told yet". It was analysing the reasons why some people do this.
It explained that all governments do this disaster planning, and have been doing it for years, including ours, but that before the pandemic ours was not given the same focus and thorough revision that other countries's plans have, hence us not being terribly prepared for the pandemic. Also, technological advancements of the last few years have meant that cybersecurity has become much more of a focus. As others have mentioned climate change is bringing extreme weather and this has had an effect on crops around the world, something which I think the National Audit Office found last year that we are underprepared for. So post-pandemic there has been a lot of work done by the government to try to bring us in line with other countries, and of course now and again there will be a press release about it.
With the result that the tabloids seize upon their chance to sell a few newspapers/generate some income online by deciding that this piece of information needs to be on the front page instead of appearing as a small factual paragraph a few pages in. All the better if it appears alongside words like "chilling" or "calamitous" or some other emotive adjective. Then these type of threads appear, because people are just reading the wrong sources, putting 2 and 2 together and making 5.
It's ALWAYS been sensible for households to have some extra supplies of food and water in for short-term need in the event of a severe weather event, power cut, illness etc. The government has advised this for years and years. It's nothing new. Just because public information is tweaked every now and again to stay in line with technology or world events, it doesn't mean that a disaster is imminent in the next month or two.
As a few people have mentioned, though, I don't think it's any coincidence whatsoever that a general election has just been announced. Unsettle people, make them look to the people in charge for reassurance, and each side will use the pandemic for their own argument. The Tories will try to suggest that they led the country successfully through the pandemic and they "protected the NHS". Labour will bang on about Partygate and hypocrisy and the upset to the economy. It's going to be like watching 2 schoolkids arguing over whose fault it was that the school guinea pig got out. I can't wait. 🙄