The period in December before the GE is not really relevant. No government could have been expected to respond then, since nobody had recognised anything unusual was going on until a cluster of pneumonia cases was reported towards the end of the month (earlier cases were identified retrospectively) and the virus was not properly identified and sequenced until early January. There was then a period of a couple of weeks when China should have acted more quckly, not hushed up its whistleblowers, and been much more open about the probability of human to human transmission. The WHO can't be blamed for simply reporting the information they were getting from China, and by the 22nd they had done their own investigation and announced there was evidence for human to human transmission. By the end of January, publications had begun to appear in major journals about the severity of the illness, the WHO had declared a Public Health Emergency of International Concern, cases had appeared here and elsewhere, and countries from the UK to South Korea were applying the 'test, track and isolate' strategy that the WHO and other public health experts had advocated for decades. Every country outside China got the same information at the same time.
While South Korea continued with this policy, ramping up its testing and contact tracing efforts to cope with the expected demand and managing to suppress a major outbreak, policy in the UK took a different course. Rather than using precious weeks in February and early March to build up a strong capacity for testing and tracing, it was decided that, beyond a certain point, we would move to a 'mitigation' stategy where (as with a flu outbreak) there would be no further attempt to contain the epidemic. With out modest testing and contact tracing capacity exceeded, we had abandoned containment by 12 March. This, I think, was the big failure of policy, and it was compounded by the effects of NHS funding cuts over the last decade, and a failure to learn from our own pandemic planning excercises and the responses to SARS and MERS outbreaks in other countries. Between the end of our attempts to contain the epidemic and the start of the lockdown on 23 March (in reponse to alarming projections of the cost of relying on 'herd immunity'), tens or hundreds of thousands of people would have become infected.
This is not just about hindsight. Many experts were alarmed at the time the decisions were being made:
https://www.theguardian.com/commentisfree/2020/apr/15/uk-government-coronavirus-science-who-advice
https://www.theguardian.com/comment...st-britain-herd-immunity-coronavirus-covid-19
https://www.theguardian.com/commentisfree/2020/mar/18/coronavirus-uk-expert-advice-wrong
https://www.theguardian.com/comment...in-failed-prepare-mers-sars-ebola-coronavirus