I think firstly I find it strange that people think other countries don’t have a right and leftwing politics. Secondly you are allowed to think things regardless of what ethnicity you are, there is a strange idea that permeates primarily the left that ethnic minorities must perpetually be beholden to left wing politics.
Talk to people who migrated in the 50’s onwards, what was attractive about britain was things like the rule of law a belief that justice wasn’t dispensed based on random biases (your religion, your caste, you tribe), that they could build something (many people come from areas of the world where civil rights around things like property ownership are fragile), thats they could better their lives and the lives of their descendents. Many arrived in britain when living on welfare wasn’t an option and you had to be a real self starter to get here in the first place so most had a real work ethic, most wanted to become british, many have traditonal and conservative personal values (family oriented, restraint, self regulation, often religious to varying degrees).
In light of that why would you think the children of migrants would be super left wing and laissez faire. Open borders is a capitalist wet dream as well, I never get lefties who argue for it. Limitless supplies of labour.
On this pull the ladder up behind them, is anyone seriously suggesting open borders. Pretty much everyone I know thinks there must be a limit somewhere. People may differ on how many but very few people want open borders. Some people actively don’t want people from their home countries because they worry about ultra conservative values being imported (can think of a few ex muslims like this).
Fundamentally if you believe having a migrant parent obliges you to hold specific political beliefs and that diversity of opinion is unacceptable then you are infantilising ethnic minorities and you simply don’t see them as british as their white compatriots.