I don't want to comment too much on the rumours about military deployment that are going around, but I've just come for a walk with the kids around my small village (just outside Sheffield) and two military helicopters have just flown over very low and very loud.
Not going to jump to daft conclusions, but I've never seen it before. Worth noting for just how utterly unnerving it felt as much as anything..
One of the things you'll find is that, as soon as something like this is in swing, people will start seeing the military *everywhere* and taking that as a harbinger of imminent military involvement. You'd be amazed at how many small military readiness exercises, QRA shouts, low-level training, live-fire exercises etc. go off every week of the year, and in normal times they just tend to fade into the background.
For example, just last week I was photographing a cross country. A four-ship of F-15s (operating out of Lakenheath, in England, going by the tail codes) came low and loud from the north, having clearly just been running a low-level sortie through the Highlands low-fly-area. I've never seen them up this way before, but speaking to a few contacts later it seems to have been a standard sortie, and they just ended up using the Highlands LFA (I think the Mach Loop in Wales is out of favour at the moment for a few reasons). That's the kind of standard movement that can catch people unawares, and in times of heightened alert it can feel like Something Significant, even if it's not.
TL;DR Don't panic too much about military movements right now, and expect any deployments to be announced properly - even if Boris and chums are in headless-chicken-mode, the military tends to be very sensitive to public perception and won't just start appearing without proper warning (obvious disclaimer for genuine need-to-get-deployed-this-minute emergencies, but we're not there yet).