It seems letting Hong Kongers in was just for geo-political purposes. If Hong Kongers are having problems getting situated in the UK as reported, it means the British government didn't really think about the impact and did it without thinking meaning posturing for the world to make it look like they're doing something. The easiest way to stop them looking bad handling people from Hong Kong is to stop them from coming. They already gave a show that they let them in. Now they can indirectly work to bar them including claiming some of them are spies which will put suspicion on all of them.
Also they believed in their own bullshit... fake news from the BBC, HK yellow media & politicans etc. claiming those wanting to leave are educated middle class with a pile of cash to spend, while there may be a few of these, a vast portion of those cockroaches arriving in UK are in fact.... cockroaches - little/no savings, little/no work skills, zero English language ability....the typical insects that live in government housing but think they're hot shit because they speak Cantonese and that limey Brits once ruled the territory once upon a time.
BoJo and Co suddenly realised.. shit, we can't really milk these roaches, while they can afford 6 months' to 1 yr's worth of rent, they're not actually buying up our shitty properties. In fact, we the UK gov., have to fork out some quid to help them speak basic English and ensure they don't cause too much trouble! Fuck it....just say they're commie spies and tell them to fuck off.