Many thanks for linking to an article from my site - the sudden flurry of click-throughs caused me to come see what was happening here, 'on the other side of the pond'.
Prepping in the UK - my goodness me, what a difficult scenario that is; my sympathies to you all. As you doubtless know, two overriding themes of prepping on my side of the Atlantic are getting far away from major population centers, and being able to arm oneself against not just the anticipated hordes of looters and gangs, but also the unfortunate starving masses who have no choice but to take whatever they can in a desperate attempt at survival.
I discuss what we anticipate to be a typical sequence of events in another article
Four Waves of Food and Shelter Seekers on my Code Green Prep site. Although written for an American audience, the underlying social dynamics are all too similar to what you'll confront.
But what to do in the UK? I read somewhere, some years back, that England has the highest population density of anywhere in the EU. Actually, a quick bit of Google-fu shows England to be the sixth most crowded country in the entire world - see this
Daily Mail article.
To put this into contrast, in England, you had 401 people per square km in 2011, and doubtless more, now. Here in the 'American Redoubt' we have a population density of 7.4/sq km in Idaho, and 2.6 in Montana. The US as a whole averages 34/sq km.
So, what to do? When considering a location for your retreat, head north, to the Highlands, would be my suggestion. With an average population density of 67.2/sq km throughout the country, and massively less once you subtract out Glasgow and Edinburgh, you start to get much more sustainable population levels. According to Wikipedia, the Highlands (the exact region being not clearly defined) and the Outer Hebrides have population densities of only 9/sq km.
Remembering also that you need distance buffers from major population centers, that suggests a location in the western Highlands, well away from Inverness and safely away from the A82 and A9. Get as close to the coast as you can.
I've enjoyed quite a bit of time in this part of Scotland, so I'm not just a Yank telling you things I don't actually know anything about. Indeed, if at all possible, there's a lot to be said for creating a retreat in the Outer Hebrides, with the simultaneous upside/downside being access there in an emergency. Calmac is enough of a struggle at the best of times!
The good news is that many of the communities, off the coast in particular, already are in large part self-reliant and/or have closely held memories of when they were subsistence crofters. It would be easy for them to adjust back to this lifestyle. And the even better news is that land is cheap in those areas. Plus you have access to peat as an energy source, and possibly wind power too.
So those are some thoughts as to location. Now, as to firearms, that's not a topic I can readily offer solutions on, alas. Needless to say, with the population crush in England, any attempt at establishing a retreat there will be challenged by opportunists and looters, and all the usual suspects that I won't risk being politically incorrect by listing. The need for effective self defense in a situation where you may well be outnumbered is a huge issue.
Which brings me back to the highlands.....