Re: leave the SM as the price of reducing immigration by 70%.
The only effects leaving the SM will have on immigration.
1. EEA citizens who have been living here for 5 years will no loger have an automatic right to residence. (Presumably meaning a big bump in applications after article 50).
2. With no more freedom of movement, migrant worker numbers for the EEA will drop (given paperwork, hostile attitude and loss of value of the pound) this will will leave a vacuum which will be filled by immigrants.
3. Since our economy will likely literally be decimated (at best), there should be less demand for immigrants to take up the slack.