The BBC's revival of Doctor Who has been hailed as the return of family viewing, attracting more than 10 million viewers at its height.
But in the past two weeks, ratings have started to slip, and Saturday's episode, written by the League of Gentleman's Mark Gatiss, attracted the lowest audience since the sci-fi show returned to screens in 2005.
Just 6.3 million viewers saw Maureen Lipman's performance as an evil alien, feeding off the minds of people watching the Queen's coronation in 1953, in the seventh episode of the 13-week series.
Two weeks ago, the return of Doctor Who's arch enemy, the Cybermen, attracted 8.6 million viewers.
A Christmas special, in which David Tennant made his first appearance as the Time Lord, replacing Christopher Eccleston, was watched by more than 10 million viewers.
The opening episode of the first series in 2005 also attracted an audience of nearly 10 million. Scheduling could be to blame for the current decline in viewers. The first of two episodes featuring the Doctor's arch-enemy the Cybermen was delayed when the FA Cup final between Liverpool and West Ham went to penalties.
The following week, the programme was again shifted in the schedules to accommodate the Eurovision Song Contest and ratings fell to 6.9 million. The World Cup may force other scheduling changes.
Doctor Who is also facing stiffer competition from ITV1, which last year lost out when it ran movies against the BBC drama. In the past couple of weeks, ITV has put in strong performances with the Prince's Trust 30th anniversary concert and Soccer Aid starring Robbie Williams.
A BBC spokeswoman insisted there were no concerns about the show's ratings. "We're absolutely delighted with how the show is doing," she said. "Week on week, it's continuing to outperform its competition."
The BBC's consolidated figures show that the first four episodes of the second series have outperformed the 2005 audience figures.
But unofficial viewing figures suggest that ratings for the second series are slightly down, with an average of 7.7 million viewers, a 38 per cent share of the available audience.
In its first seven weeks, the 2005 series averaged 7.9 million viewers, a 39 per cent audience share.
The revamped Doctor Who has been widely deemed one of the BBC's biggest successes of the past two years, despite Eccleston's decision to quit as the Doctor after just one series.Reuse content