Capt Scribble, a couple of months ago is possible. November/ December is not possible. I suspect it started in China in October but we are more certain about start dates elsewhere in the region. That makes the UK impossible in 2019. As a separate calculation we can model backwards from the known cases at any point to work out the time of first transmission. Above my paygrade and not that accurate but you dont get to the start of 2020 for the UK. The difference with SARS-CoV2 is that is transmits effectively so you rapidly get a cluster ie 10 or more cases and rapidly increase numbers. You cant get just one case now and one case in a month - unless of course you have an efficient healthcare service that can track and trace....