I mean, absolutely; if the desire is to have fewer people, tanking the economy will certainly help. The primary reason that the UK (and Germany) have high rates of immigration is that they're desirable places to be from an economic standpoint, and the continued economic expansion of those countries requires immigrants. The UK unemployment rate is very low; the people moving to the British Isles are doing so because there are jobs to be had, and jobs that need to be filled. It's a mutually-beneficial arrangement in the main.
But, I mean, if the goal is to tank the economy in order to make the UK less appealing to immigrants, there has to be a more entertaining way. Like, bet the national budget on Saints to win the PL in 2019-20 or something.