I'd kind of assumed that with every going a bit tits up for Darius - the guy from the flats being arrested, TLR wanting to kill a police officer - he was too busy to turn up to a interview with some journalist. He was probably having an emergency summit with his brother and his henchmen about how to deal with the TLR problem.
Alternatively, we know that Sally Wainwright changed the events of the final episode, so that probably means she had to go back and change events in the previous episodes. Maybe in the original script Darius and Richard met and different outcomes ensued.