I see EURACTIV is currently reporting that COVID 19 was evident in Spain in March 2019, so there can be little doubt if that's true it was also seeded here in the UK way before last January and it would also indicate that the level of infections has been way above the currently published figures.
I have mentioned before that the lockdown could/should possibly have been much earlier (not just 1 week) as has been mooted over the last day or so. I still maintain that the level of infection in this country was way out of control by the end of March seeded by people returning from holidays abroad and by people not showing any symptoms. It follows that the advice given by Sage was flawed and it wasn't just poor decision making that's at the root cause of the number of UK deaths. The 250,000 or declared coronovirus cases in this country are, in effect, just the number of hospital admissions. I think the number of actual cases in this country will be shown to be far higher with the range of estimates currently running from 2.6 million to 19 million. At the moment the BBC is showing that just over 7 million people have been infected wordwide with 412,000 deaths. Its possible that the UK alone could have had over 7 million infections. Add in population densities, ethnic mix etc and then you might have a more balanced picture with regard to the overall impact on the UK