Episode four of the Arthurian drama pulled in 5.92m (25.6%) for BBC One over 45 minutes from 7.05pm, a rise of 160,000 on last week. Merlin followed on from Strictly Come Dancing, which suffered from being scheduled at the earlier time of 5.50pm. This week the ballroom show averaged 7.42m (34.6%), a week-on-week fall of 1.8m. The audience grew throughout its 75-minute run-time, however, reaching a peak of 8.88m (37.5%) at 6.55pm.
ITV1's live coverage of England's World Cup qualifier against Kazakhstan at Wembley brought in strong ratings, with an average of 6.28m (35.5%) watching between 4.30pm and the start of The X Factor at 7.15pm. The game, which the home side won 5-1, peaked with 8.97m (38.8%) at 7pm. Ratings figures do not take into account the audience watching in pubs, clubs and bars.
The X Factor's first live show of the year pulled in a strong 10.36m (44.1%) over two hours from 7.15pm, with a peak of 11.25m (48.5%) at 7.50pm. The figure is up considerably from the equivalent episode last year, which had 6.17m (30.5%) in an earlier, 5.30pm timeslot.
All Star Family Fortunes followed at 9.15pm with 6.48m (29.3%), then The X Factor Results Show had a strong 8.02m (40.8%) over 45 minutes from 10pm.
After Merlin, BBC One suffered for the rest of primetime. The National Lottery: Who Dares Wins was down to 4.42m (18.9%) at 7.50pm, then Casualty had 4.88m (20.7%) over 50 minutes from 8.40pm. 3.61m (16.3%) watched a news update, then 2.39m (11.5%) saw a repeat of Little Britain USA at 9.50pm.
Overall during primetime, ITV1 had a gigantic 39.2% audience share, up from last week's 28.8% and more than double BBC One's 18.7% (last week: 26.6%).
Channel 4's live coverage of Building of the Year went largely ignored, with just 0.54m (2.3%) tuning in from 8pm. The Arnold Schwarzenegger film Collateral Damage was a more popular choice, drawing 1.43m (7%) between 9pm and 11.05pm.
Five had 882,000 (3.8%) and 1.07m (4.6%) for an NCIS double bill from 7.35pm, then the audience rose to an all-day high of 1.41m (6.7%) for CSI at 9pm. Law & Order: Criminal Intent closed the night with 812,000 (5.2%).
BBC Two logged a share of 7.4% during primetime (last week: 6.4%), ahead of Channel 4's 4.7% (5.7%) and Five's 4.6% (5.2%).
Two helpings of The Xtra Factor brought in predictably high audiences for ITV2. The first - broadcast between ITV1's two live shows - had 924,000 (4.8%), then a post-results reaction show managed 984,000 (7.5%) between 10.45pm and 11.30pm.
Sister channel ITV3 also had a good night, with 527,000 (2.6%) watching a two-hour Marple at 7.15pm. Taggart then picked up 501,000 (2.7%) over 90 minutes.
> Click here to read our review of last night's Merlin
Ratings data supplied by Attentional