Well I'm one of the enthusiasts who had attention from the BTP once (as did James, he was with me) at London Bridge, back in 2005 IIRC. Apparently someone thought we were acting suspiciously (taking a photo here and there as well as writing down all the stuff that came through) and alerted them to us. We got talked to, they had a quick look in our bags and the photos I'd taken and gave us a pink (I'm sure it was pink, maybe white. I had it in storage until 2007) slip each. Not exactly a stop-and-search but close enough for me.
One point I MUST raise is that these officers were most pleasant and polite and perfectly happy to tell us why they came to see us. I swear the one who had a look at my notebook (I showed him what we were writing, plenty of 465s, 466s, 376s and 375s in the time we were there!) nearly had his eyes pop out of his head at how much I'd written down!
So yeah, not all of them are nasty beggars, we had friendly ones so some people just must have had bad luck.
As for the article, I read it tonight after my sister told me of it. In my eyes, it reads a lot like that article about flailing The Daily Fail (sorry, Daily Mail

) ran the other week. Mis-informed and a lod of codswallop.