The Beast Below was watched by 6.7 million viewers, according to unofficial overnight figures.
The programme had an audience of 6.4 million on BBC One, with an additional 330,000 watching on BBC HD. The programme's share was 34%. Although a drop on the previous week, the programme was still the most watched of the day, beating the second-placed National Lottery by 0.8 million viewers. It is very rare for a programme placed so early in the evening to top the ratings for the day, especially on what was, wether-wise, one of the Saturdays of the year so far in the UK.
Harry Potter and the Order of the Phoenix performed the best for ITV1, with 5.7 million watching the network premiere. The FA Cup had an average of 3.3 million viewers, with a peak of 4.9 million against Doctor Who.
The highest peak of the day was between 4.15pm and 4.30pm when 7.6 million watched the Grand National horse race on BBC One.
Overall, the programme currently stands as the twelfth most-watched of the week, with Sunday's ratings still to come. A top ten place is still a possibility once the final ratings are calculated next week.
On BBC Three, Doctor Who Confidential was watched by 0.56 million viewers, a 2.7% share of the audience.