The Eastern Europeans, the Poles in particular, are not "a drain on the country's economic security". Quite the contrary, they're net contributors: mostly young, hard-working, with useful skills and not claiming benefits. Rather similar, in fact, to the situation with the Hong Kong immigrants which you describe.
I don't know a single Eastern European claiming benefits - and I know a few because my girlfriend is Czech.
To be honest I expect many Eastern Europeans will eventually go back to their original countries. That's the impression I get from the people I know.