I think there are a few (unjustified) leaps of logic in the above thread.
Firstly, the published information states there is no strategic plan to increasing the visa waivers to the UK. I think
@Cloud Strife may be thinking about the advance passenger information system that is about to be introduced. Critically, and exactly the same as the system in the US, this will not produce a decision on whether a person will be allowed into the UK. It is an extra step that any passenger coming to the UK will need to go through, and the only assurance it will give passengers is that their carrier will let them board (it is likely that carriers won't allow people to board unless the advanced information is registered). The important thing to remember is that there will
always also be a later decision as to whether the person will be allowed into the UK. At the moment, those decisions are sometimes made according to an algorithm at an eGate. But even at eGates, it is sometimes required for an immigration officer to make a decision on whether the person will be let in or not - that is not always apparent to the user. In other cases, the fact that a decision is being made is more obvious because you are standing in front of the immigration officer. Those decisions are not automatic - the immigration officer has to use judgement. All Immigration Officers undergo a level of security vetting (which requires you to live in the UK for a certain amount of time, and serious and continuous background and place checks) and, unless I'm very much mistaken, they have to be a UK citizen. Can you imagine the issues that could happen - not least political - if the person who was making a subjective decision about whether a person should be allowed to come to the UK didn't themselves have the full right to come into the UK? Or the person who was deciding had an expensive vice, and 'friends' who would be willing to help them out for 'a bit of help with their visa', and there was no way of reliably knowing?
Other posters have described non-UK nationals doing processing work on visas outside the UK. But importantly, they are not making subjective decisions. Those decisions are made by UK citizens, who are working under the protection of diplomatic immunity, to reduce the risk that outside influence can be brought to bear on those decisions (and there are frequent attempts to subvert the system by people who don't want to play by the rules). Even if decisions on visas were made by locally employed staff, a visa is not a permission to enter. It is quite possible to have a visa issued, which when the person gets to the border, the immigration officer decides that the person should not be let in. It's rare, but it happens.
So, this is why, when there are juxtaposed controls, it is an immigration officer (UK Citizen, security cleared, very closely monitored) that is making a decision as to whether a person should be allowed to enter. That is never going to change. And every country (or single immigration area) does it exactly the same way - for the same reasons.
So going back to why this was raised. Wherever immigration controls are, there will need to be a UK immigration officer. And if you don't want long delays, you'll need a few of them. And they are super expensive - as noted above, while their headline wage might not be high, their total cost will easily be getting into 6 figures for each person, especially in the case of juxtaposed controls.
It is, of course, attractive to imagine a time when the borders wouldn't need such painful and expensive bureaucracy. But the sad reality is that the minority of people who want to abuse the system means that it needs to be run in a labour intensive way.