Does any British political party have a rational immigration policy?

Immigration, so we are told by some commentators, played a key part in the slim majority in favour of Brexit in the Referendum of 23rd June 2016.

It occurs to me that no UK political party has produced a detailed objective analysis of the economic  benefits and disbenefits of different levels of immigration.

David Cameron's commitment to reduce net annual immigration to the "tens of thousands" is discussed at length in the media.

But nobody, so far as I'm aware, has asked the serious question of whether reducing net annual immigration to the "tens of thousands" is beneficial or harmful to the UK economy.

I've sent a couple of Freedom of Information Requests to see if Government Departments have looked at his important question and what answers, if any, they've arrived at.