This five-part mini-series started superbly. A dramatic first episode, full of incident, laid out the main themes and built up the tension. The next two episodes maintained the tension, developing the near-future main storyline about a surveillance society and its impact on citizens. Robert Carlyle appeared (and disappeared), as threatening as only he can be and kept the excitement level high.

But then it faded away. The plots became too convoluted, with too many themes and unresolved or unnecessary twists – notably a scene where Carlyle creeps into a house and downloads a laptop. What was that about? And the final episode was so disappointing – it was as though the writer (Peter Berry) had only enough material for half an episode. So the pace slowed down, the increasingly unconvincing love story took over, with long, lingering and time-wasting glances, and the main surveillance theme sank under the weight of biological, genetic and political extra plots that led nowhere. It could have been a gripping thriller if it had been stripped down to a feature-length film but in the end it only left the feeling that five hours had been wasted. And this is despite excellent performances, particularly by Benedict Cumberbatch, Robert Carlyle and Geraldine James - the script could not match their talents.