I'm also in the UK and a friend brought up the illegality of it once, when we were discussing it, so I ended up having a look and it's freely available and sold by Amazon.co.uk, so I think your fears are exaggerated.
I was trying to find a balance between not exaggerating the risk, while also letting people know that you have to be a little careful when viewing / downloading this in the UK.
If you have cloud backup enabled and you download this then expect to be put on a watch list. If you share this link publicly on social media then expect to be visited by the police. It might not happen of course, but you should expect it.
And you've already been in trouble with the authorities for posting something politically incorrect on social media then possession of this book could quite easily be used against you.
Even if the risk of getting caught and sentenced is minimal the fact that it can be used against you is enough to be a concern. If nothing else it indicates a problem with UK law that should be solved and the fact that children have gotten caught up in it should worry everyone who cares about their freedom.
I have purchased things on Amazon that were illegal for import. I didn't know it at the time of purchase. I only realized months later when I wanted to buy it again, only to find all the listings were gone.
With so many 3rd party sellers it isn't too surprising.
Well, the paperback edition appears to be sold by Amazon.co.uk and it's also available as a Kindle edition, so I don't think importing it would be an issue
There's an instance where two teenagers were charged with possession of it, but were found innocent: http://news.bbc.co.uk/1/hi/england/bradford/7685636.stm
However, if you're also involved in terrorist activities, then possession of it could count against you.