I don't think people are actually against immigration, a major part of it is with the 'type' of people coming. That comes from the continued post-Brexit sentiment of xenophobia and now the new rejection of multi-culturalism.
It started years ago with the perception that people in Europe were coming and taking our jobs, the jobs that we couldn't be arsed to do anyway. It's just founded in a complex mess of racism, stupidity but also successive years of government mismanagement of immigration policy versus what is actually needed.
I still have to ask why on earth people would want to come here. The weather is shite, the pay is shite, the working conditions are shite and a significant number of the people here are moaning bastards who hate immigrants.
I was born here and if Australia, Norway or Canada came calling then my bags would be packed!