UKBF allow airlines to let their own staff do the initial screening rather than insisting everywhere has an outpost of British Immigration officers
Quite so. E* could do adopt this procedure if they so wished. But they don't because that initial screening still requires check in, luggage screening, sterile areas etc
and immigration control on arrival in London, with the space requirement and delays to passenger journeys that would entail. Having British immigration officers at Paris, Brussels, Lille, Amsterdam etc adds little to the Check In procedure but is much quicker on alighting. Plus no need for a huge immigration hall at St Pancras (where would that go?)
What really needs to happen is for Eurostar (and any new Channel Tunnel operators) to operate like 99% of other railway borders around the world and just stop the train twice (once on each side of the border) for border control. For the Southbound trains you would do UK exit control at Cheriton and do Schengen entry control at Coquelles. For the Northbound trains you would do Schengen exit control at Coquelles and do UK entry control at Cheriton. This would slow down the journey (you would probably need to stop for at least thirty minutes on each side so about an hour total) but that would be made up by the fact that you could just arrive at the station five or ten minutes before your train departs. There would no longer be a need to arrive 60 minutes to 90 minutes early if they did border control onboard and scrapped security.
UK Border Agency would not agree to such an arrangement. E* would still have to check in and screen passengers before departure (there can be no possibility of an undocumented or incorrectly documented passenger arriving at Cheriton), so you would still have the check in and a minimum check in time. I doubt UKBA would agree to check passenger's passports in the carriages - they want passengers to present themselves standing at a counter / machine like the airlines, and they would want to check that no-one is hiding under seats etc, so it would have be empty carriages for that to happen. Quite aside from some passengers wanting to go to the toilet, the buffet car etc during the enforced stop. Nor will they want the inevitable confrontations with sometimes desperate people in amongst a load of seated passengers.
Why would E* want their trains to be delayed 60 minutes in each direction, costing more trains and staff and damaging their competive advantage over flying? Yes, some people turn up only 10 minutes before train departure, but most won't and will not appreciate the intermediate delay.
n each side so about an hour total) but that would be made up by the fact that you could just arrive at the station five or ten minutes before your train departs. There would no longer be a need to arrive 60 minutes to 90 minutes early if they did border control onboard and scrapped security.
Also the rules about security are nonsense. They should completely scrap security. It is nothing more than a theatre. It is even more bonkers when you realise that Eurotunnel car passengers (who go on trains through the same tunnel) do not have to go through security. Similarly car passengers on all the cross channel ferry routes do not have to go through security either. There is absolutely no need for security.
Doing this would solve so many of the issues that are preventing Eurostar from expanding and preventing other operators from starting new services. You would no longer have the issues of new Mainland Europe destinations needing border control and security set up. You would also no longer have all the London Saint Pancras capacity issues that they keep talking about. You no longer need all that extra space without border control and security. It seems like a no brainer but yet it never seems to be considered.
You might think the security is all 'theatre' (a word commonly used to denigrate security checks everywhere) but so far it has prevented a bomb going off in a E* train in the tunnel or elsewhere. It will be a brave politician to take that decision to scrap it, and wobetide their conscience if an incident subsequently occurs.
What you suggest seems like a 'no-brainer' but of course it has been considered and ruled out by the people with the brains.