You missed out blatant incompetence?
You really think they allowed in vast numbers of immigrants through sheer incompetence?
I find that a stretch, even for the Tories. You see it would be positive incompetence, not an oversight. Those visas don't issue themselves.
I think the whole thing needs to be looked at
very seriously. I would start by expanding our training for doctors, dentists (above all), nurses, IT engineers and other essential professions. We ought to be producing enough of these, or at least 95% of the requirement. However, I know this means more expenditure and thus, at least in the short term, higher taxes. It's also something that by its very nature will take time to kick in. Say two years to set up, at least five more to have any real-world impact. During which time, you'll be paying extra tax. For, on the face of it, nothing. Not an electoral dream, is it?
The next question is whether there are enough of us, generally, to serve the needs of the economy. I would start by encouraging more childbirth, spending a lot more on education and training - not least on those above school age but in idleness - and (sadly) I would feel duty-bound to increase pension age. Though that last might involve some restructuring (very socialist this) to ensure that people over (say) 55 are guaranteed jobs that they are fit to perform. (It could not be left solely to the market.)
Again, much of this would be medium-term, and most of it would be costly. (You know what that means.)
The X-factor in this algebra is whether we would still have to import some labour to maintain the economy. I suspect we would, but I don't pretend to have the figures. Truth is, if the economy fails due to a shortage of labour we are all fucked.
In short, to solve this issue, you need government intervention and a great deal of public expenditure. And no politician has the bollocks to say this, or even to set out the facts. It's so much easier to whine about people in boats and stir up resentment. That's not just cheap, it costs almost nothing and is very easy to administer. A politician's dream. Say the right shit and people will even vote for you.