Old Geezer
Go for a walk in Dorset or Wiltshire or Lincolnshire and come back and say we are over populated.
The requirement for all of the things you mention drops as population does and without immigration population in this country will fall.
Without immigration in 40 years time there will simply not be enough income generated by working people ( or working people themselves to look after the older people)
You may not care (depending on your age) but some of us are planning to be about then and may need a plumber or doctor or even get our bins emptied.
What we don't need is the sort of economic tourism of people coming over working a year or so and sending all their earnings back overseas.
We need good quality people coming here and bringing their families.
This is why the Government introduced a points based system for immigration two years ago
http://news.bbc.co.uk/2/hi/7269790.stm