Corrected entry: Why do the infected travel in groups? Wouldn't they attack anyone they see if they had pure rage? Not just the healthy people.
Corrected entry: They leave Hannah and Frank's flat in Canary Wharf, drive through the Blackwall Tunnel going South and get to the north of England without crossing the river again. Manchester is north of the River Thames, as is the flat - they have no need to cross the river and go completely the wrong way yet still get near Manchester. (00:41:15)
Correction: Canary Wharf is an office block, so it is unlikely that Frank and Hannah could live there. Therefore it could be possible that their flat was south of the river.
Whoever wrote this is not in the UK. Canary Wharf is not just an office building. There is lots of living residences on the Isle of Dogs. The main comment is correct, they had no reason to take a tunnel taking them south of the Thames when they were north of the Thames to begin with.
Correction: They don't travel in groups. They are all attracted to the same stimuli, much like sharks to blood. Simply because they all end up pursuing the same target at the same time does not suggest they are constantly roving in packs. They could easily be wandering around and run towards something making a noise, and would simply end up with a group of infected doing the same.
So what is the stimulus intended to be? Noise? Bleeding? Sweating?
The infected individual is driven by constant, rabid, all-consuming rage, with a single-minded drive to always violently attack and pursue any uninfected individuals they find.