But seriously, the people who usually bring up immigration isn't really thinking about the UK as having too much people.
Those people are just more worried about a particular race (e.g. Eastern Europeans) coming over and blame them for all their wrongs.
If it was "really" about immigration (i.e. how much people in this country), they would be screaming about overdevelopment in cities or countys as well because that is one consequence of immigration (i.e. having more people) - but they don't. They are more worried about the foreign faces they see when they are down at the local shops.
And therefore all the parties have stupid policies.