Originally Posted by
TWA884
That's a TSA rule.
In case that you missed it, my point was that it's less of a hassle to transit at some airports, such as HEL, than at LHR.
In the very same way you’ve just referred to a TSA rule as an explanation for inconsistent treatment, it is a UK requirement that you go through transit security for all bar domestic originating transfers.
Don’t get me wrong, I don’t agree with it and would much prefer the UK establish a white-list of equivalent regimes where transit security isn’t necessary, but as it stands LHR are just implementing government policy.