There’s a simple explanation for this. Being “tough” on immigration would be bad for the economy, bad for the NHS, and bad for the country as a whole. So once a party is actually in government, they don’t want to do it, whatever they said in order to gain votes during the election campaign.
You missed one important point: A rational party, or at least one with a rational leader. If you're dumb enough you will go through with it no matter how much it hurts your economy, your health system, and your country as a whole. I'm not in the UK but maybe someone from there could provide an estimate, on a scale of 0 to Trump, where does Farage rate?
But on the other hand, claiming that, as mentioned, any alternatives to high immigration is bad for the country has to be BS because it does not pass the "smell test". I never understood this stance that countries must have high immigration, that high immigration is good (TM) and that anything else is bigoted and racist. Best theory is that anti-racism has mutated into a monster mixed with business interests only interested in an ever growing labour and consumers pool.
