The rules on which they entered in 1972 were changed in 1981.
These days, how can asylum seekers enter the UK? It is not possible to apply from outside the country, and there is no asylum visa. Therefore, to claim asylum in the UK a person must enter either irregularly, such as by small boat, lorry, or by using false documents, or for another purpose, such as tourism or study. Others could arrive without a required visa.
We have changed the rules, forcing people into these dangerous boats. Those people are a mix of genuine asylum seekers and illegal immigrants - both are lined up for export to Rwanda as if they were the same, and the protestors in the OP are trying to separate one from the other.
As I said, without the protestors, and in 2022 rather than 1972, Priti Patel's asylum seeking parents would find themselves in Rwanda. And she knows it ...
https://www.independent.co.uk/news/uk/politics/priti-patel-immigration-laws-parents-home-office-brexit-a9343571.html