Public Health England, April 2020: “Some of these patients may have COVID-19, whether symptomatic or asymptomatic. All of these patients can be safely cared for in a care home if this guidance is followed.”
From Page 4 of this Public Health England document dated 2nd April 2020:covid-19-care-homes-guidance-1
From that PHE document:
So the UK government knew by February/March 2020 that SARS-CoV-2 infections could be asymptomatic, yet they still allowed infected patients to be discharged into care homes.