The UK is connected to continental Europe via the Channel Tunnel. We rely on an endless stream of trucks coming across from the continent and driving directly to destinations throughout the UK with their original drivers to supply us with important things like food, and they often then go on to do delivery trips within the country. (One of the big reasons that Brexit is supposed to be such a disaster is that it'll disrupt all this. With the scale at which this happens, even a small delay to each truck is apparently enough to cause massive disruption.)

Remember, this is a very good way of spreading Covid-19 to new areas - it's almost certainly how it got into Beijing, which was the best and most aggressively protected city in all of China at the time.