This is perfectly rational. Do you trust political polling from pollsters with party affiliation? I hope not.
Over the last couple years, I've started mentally putting a "P(BULLSHIT)" next to every source I read. The estimate keeps growing.
While you might want to make this an ad hominem attack, all I can say is that my probability estimates are pretty darn bipartisan.
Isn't usually the most "esteemed" establishments that are closer to the party line?
That's par for the course of being "esteemed".
I don't know them, but I'll take your word for it. However, will point out that it is in no way worse than the source you provided (no source)
How about Migration Watch?
https://www.migrationwatchuk.org/statistics-population-count...
Compared to the total non-UK born population, Pakistan + Bangladesh are a tiny blip.
Another source:
http://www.telegraph.co.uk/news/general-election-2015/politi...
More from the ONS:
https://en.wikipedia.org/wiki/Foreign-born_population_of_the...
What figures do you believe are accurate?