The second episode was down 900,000 viewers on last Tuesday's opener, but that fall isn't particularly surprising when you consider every episode of the new series has since been made available to watch online via the BBC iPlayer.
Our Friend Victoria followed the latest episode of Car Share with 3.7 million viewers, down over a million on last week.
Earlier on BBC One, Holby City was up 200,000 viewers on last week to 4.7 million while EastEnders continued with 5.7 million.
Over on ITV, Emmerdale had 5.5 million viewers while new panel show Don't Ask Me, Ask Britain struggled with its opener pulling in just 1.8 million.
Pushed back to 11PM as a result of the General Election announcement, Dermot O'Leary's second day in charge of The Nightly Show this week had fewer than a million viewers.
Elsewhere, over on Channel 4, First Date returned to over a million viewers but was eclipsed by One Born Every Minute which had 1.2 million an hour earlier.
Channel 5's most watched programme of the night was The Yorkshire Vet with 1.7 million while over on BBC Two, Bake Off: Creme de la Creme dipped to 2 million viewers, down 200,000 on last Tuesday.