To answer the title question - probably never as long as society remains so litigious, and while taking more and more responsibility away from the individual. GWR has always been worst, and they also (as far as I know) are the only TOC to use 40 seconds as their 'doors will be locked' time, rather than 30. While the issue of whatever margin is used is for another place, a standard time would surely have been within the capabilites of the TOCs to agree on. Seemingly not, and I can't see much changing despite promises from GBR or whomever. This is the group of railway and/or police management that spawned "see it, say it, sorted", remember, so the outlook is surely grim.