If we can firm up our borders and control immigration better, then that will be a big improvement for a start. We need skilled, non criminal, checked workers who can add to the quality of life here not diminish it. There may be a positive impact on wages for people already in the UK if we can stop the flood of unskilled minimum wage types coming from Eastern Europe.
Everyone just talks about economic impact but 250,000 extra people a year is putting ridiculous strain on transport, hospitals, welfare and care services and schools etc. Not to mention housing stocks, rental costs, water supply, criminal activity/policing, potential terrorism surveillance, pollution and the environmental impact.
It doesn't help of course that any economic benefit from these extra bodies seems to be swallowed up into the same channels of the super rich and public funding for everything is continually cut.