Revealing mistake: When Jim is walking across the Westminster bridge and shouts "Hello?" for the first time, in the next shot you can see a blob on the bridge (right of picture). This is all that's left of a car going across the bridge, that wasn't painted out completely.
Factual error: In the scenes driving to Manchester the motorway is completely clear of traffic, no abandoned vehicles of any sort. With an outbreak like this happening the motorway would be gridlocked.
Other mistake: When Jim, Selena, Frank and his daughter enter the supermarket, you can notice all the fresh produce (apples, carrots etc) looking fresh. This virus has been going on for a few days now, and supermarkets get their fresh produce out immediately. After 10 days or so, give or take, the fresh produce shouldn't be looking this fresh. (00:46:00)oobs