you thought politely asking someone to move so you could exit the train would startle them? and then you thought you might do it in a fake british accent?
Yes and yes. It's uncommon where I live to talk to people on the train - and being a bulky 6'4 male, whether I like it or not, I have a lifetime of experience that it's startling for women when I appear behind them without them realizing. It was a passing thought I found funny in the moment. I think it might say something about the reason why some segment of the population is apparently doing this.
Most British people I know in this situation would literally just say, "Sorry!", just loud enough for the person blocking hear you so that they move and reply, "Sorry!".
In general I think we don't like to converse too much, especially on public transport.
When I first visited Britain what stood out the most to me was how much chitchat there is between strangers in public places, especially on the train. Something I hadn’t witnessed anywhere else in Europe. Also, something that made me feel very inadequate as I just couldn’t keep up with that manner of communication. A Canadian friend had noticed the same.
Granted, it’s mostly the colder parts of Europe that I have the most non-tourist experiences with. So that’s that.
I don't know if it's Gen Z specific but I think people now just have a very difficult time interacting with strangers in public. It's kind of a bizarre phenomenon of the digital age.