Sean and Lale blowing up a tower in the middle of the city of London without the city going into full lockdown and police being everywhere.
Lale and Sean killing the newly elected mayor of London. These two are full blown terrorists at this point and paired with Lale's background of supporting Kurd militants with drug money this really could spawn a British-Kurd conflict.
Shannon killing a cop in her own home too, particularly noteworthy because she got on her brother's case for merely keeping a gun on him for protection back in the first episode like
'Is this what you've become now?'
Nobody wearing gloves or masks or anything at any point either, DNA has to be on literally every scene if anyone bothered to do a proper investigation.
Hell, that government secret agency couldn't even find the tooth chip on Elliot and they had him in custody taking samples from his hair, skin, clothes, everything.