Question from an outsider, is the genuine political consensus amongst the people of Britain that they’d rather die out and go extinct than admit anyone not British to the country? Because managed decline and eventual extinction seems to be the platform of every major party.
I don't believe there is a consensus for that. Many of us have immigrant ancestors, have married immigrants or have immigrant relatives. Britain is a mongrel nation, always has been. What we seem to have at the moment are lots of politicians and the media pushing an anti-immigrant agenda.
and no one getting airtime to promote the benefits of immigration, and how we all gain. And also, there are no major figures out there speaking some home truths about what will happen to our economy if we continue to demonise those that come here to work, to live and to seek a better life.
i think the genuine consensus is that we can afford to be a bit more racist and then make immigration more brutal if it wins some election or helps some other policy marginally
Short answer: no
Longer answer: there is a genuine political consensus amongst the major political parties and newspapers that we (immigrants) are the worst people. And everything is our fault. And we have an easy time.