If it were up to me I'd implement an Australian style of immigration policy. One based on a points system that was itself based on the employment needs of the nation. Simple really.
If you're a highly qualified foreign heart surgeon and we have a surfeit of heart surgeons, thanks but no visa for you I'm afraid. If you're a highly qualified mason and we have a deficit of masons, welcome.
This system is great because; a) it doesn't discriminate on the basis of colour, religion, sex, sexual preference, age, etc. and b) the most qualified for a specific task get to live and work and pay income tax in the UK. Win, win as far as I can see. The unqualified or the not required qualified do not enter.
Only people hell bent on a nation's destruction and/or want unfettered immigration because they believe it will enhance their election prospects advocate for open door immigration policies.