Ok, maybe the assumption of xenophobia is unwarranted, but restricting of immigration was one of the main selling points of Brexit.
Also, the point about age holds - under 45's voted heavily in favour of Remain (as did London, Scotland and Northern Ireland)
The bizarre bit is that they are also perfectly OK with immigration from the EU its the "other kind" (direct quote) of immigrants they don't want.
Edit: This is about 4 people in total so entirely possible its not representative.
It was a majority opinion of old people sure.
https://yougov.co.uk/topics/politics/articles-reports/2019/1...
https://lordashcroftpolls.com/2019/12/how-britain-voted-and-...
The tory party has realigned itself since 2016 to the same values of the leave campaign, one heavily based on fear of foreigners
https://hyperallergic.com/310631/the-visual-propaganda-of-th...
The BSA31 performed in 2013 shows a strong age correlation with sentiments towards immigration: https://www.bsa.natcen.ac.uk/media/38190/bsa31_immigration.p...
The BSA34 in 2016 shows similar trends in the age distribution: https://www.bsa.natcen.ac.uk/media/39148/bsa34_immigration_f...
It is entirely possible to be pro-Tory and pro-Brexit while being anti-xenophobia. But the Conservatives have been carefully-mining the anti-foreigner vote for decades (as did New Labour) and it's not plausible to argue that Brexit would have won without that sentiment: it was too large a part of the expressed reasoning of Brexit voters as a group when polled.
Now the Tories have realized that they can spew bullshit lies and win an election with minimal consequences. They also have discovered how much easier it is to game the damn failing electoral system. (e.g. in Cam I have seen Tory pamphlets pushing for Lib Dems or Labour just to split the left vote).
It was a travesty that No won the AV referendum.
Notoriously, a few years ago a former advisor to Blair went on record to say that New Labour deliberately encouraged as much immigration as possible in order to "rub the Right's nose in diversity", and:
"He said Labour's relaxation of controls was a deliberate plan to "open up the UK to mass migration" but that ministers were nervous and reluctant to discuss such a move publicly for fear it would alienate its "core working class vote".
https://www.telegraph.co.uk/news/uknews/law-and-order/641845...
It's really difficult to reconcile this history with the ideas you're expressing above. Far from "carefully mining the anti foreigner vote for decades" they were explicitly undermining it by hiding the true extent of what they were doing.
So overall, I don't see deliberately increasing migration and deliberately using dehumanising rhetoric and policy changes against (some) immigrants to shore up electoral support as being at odds. The current government is strong on anti-tax rhetoric whilst presiding over heavy tax rises. Labour wanted immigration to keep wages low and increase growth. It also wanted the votes of people who wouldn't want that. So it did the former fairly quietly, while performatively stoking up the Home Office's capacity for villainy. So is modern politics.
(FWIW 'Floodgates' is itself somewhat dehumanising, I think: people aren't an undifferentiated mass threatening to overwhelm the boat, they're just people. 'Gates' would have done just fine.)