There's something else going on here that OP @saraclara hasn't commented on. Maybe she herself doesn't feel this way, but I'm going to discuss how I've seen others behave.
I think there is a nasty, silly thing in British society amongst certain folk, where being openly kind and warm to strangers is considered less sophisticated and somehow lower in class.
Bear with me - I don't personally think this, I actually cringe at the thought - but I have seen it. I will also use "class" terms on this post to quickly explain my thoughts despite hating old class system etc.
I have worked with people, I can think of three in particular, who come from ordinary comfortable backgrounds and have decent enough jobs. They send emails and messages that are almost comically terse, as if they're the CEO with no time for pleasantries - and without fail, all three won't acknowledge people who they think aren't worthy of their time.
Person X made me laugh at work a couple of weeks ago. Receptionist on desk said "Have a great evening take care see you tomorrow" in a cheery way; I reciprocated but X just looked over and smiled thinly, then walked out. This was one of a dozen times she did this that month, and had nothing to do with personal life, mood, or anything else.
Some people just seem to despise warmth and equate it with a lower echelon or mentality. It's why some Northern folk are described with wondrous amazement by some of my Southern friends as "bubbly" or "down to earth".
I strongly believe there is a segment of UK society who want to differentiate from "Huns" as a point of sophistication rather than sentiment. Ugh.