Unofficial figures show that the first episode of Series Four, Partners in Crime, was watched by 8.4 million viewers, giving it a 39.4% share of the total television audience. It was the most watched programme of the day, beating the second placed Casualty by over 1 million viewers.
The overnight figures are slightly up on the last two season premiers, both of which benefited by being in a later time slot.
The programme got almost double the audience of its main ITV1 opposition, You've Been Framed, which got 4.7 million watching.
The audience peaked in the last quarter hour at 8.7 million, with the BBC1 audience dropping by nearly 3 million when the programme finished. Final figures, which will be released by BARB in ten days time, are likely to be higher as the programme was transmitted slightly later than its published time slot.
The programme currently stands as the 10th most watched of the week, behind several episodes of EastEnders and Coronation street.
The children's audience was 1.3 million, which was a 51.0% share of all 4-15 year old's watching.