[7] Reviewing the first episode for The Guardian, Stephen Moss began by noting the bravery of adapting a book "which film critic Roger Ebert called 'perhaps the least filmable novel [Conrad] ever wrote'".

Conrad based Verloc's attempt to bomb the observatory on a real incident in which a half-baked anarchist blew himself up, and his description of it in a later preface to the novel should be the starting point for any treatment.

In The Daily Telegraph, Gerard O'Donovan found that in the second episode, There is such a dearth of decent human beings in The Secret Agent (BBC One) that it makes for a deeply uncomfortable viewing.

Set at the precise point where political idealism and terrorism intersect, it features such cynicism at its core that, even 109 years since it was published, it feels utterly contemporary.

O'Donovan added, "Marchant's skilful untangling of Conrad's over-complicated plot brought all this to the fore without sacrificing too much in the way of subtlety or surprise", before concluding: "It could have been the climax to a lesser drama.

But with another full hour to go, the one thing that seems guaranteed by The Secret Agent is an even murkier – and perhaps still more affecting – trawl through a dark night of the human soul that, despite being dressed up in Victorian garb, feels wholly relevant to right now.