The 60-minute reality show saw its audience build over the time it was on air from 4.4 million (20.4%) to 5.2 million (23.4%) in the final 15-minutes. The show exposed Blake's attempts to communicate with the outside world through a coded message from her family.
Over the show so far, Big Brother's audience volume is up by 14% compared to the same period last year. Over the first seven days the Brighter Pictures-produced show has averaged an audience of 5 million, up from 4.4 million last year.
Last night C4 was comfortably ahead of all the other terrestrial channels by some margin, despite the programme dropping by 400,000 from the previous programme. Its nearest rival was the concluding episode of ITV1's Vital Signs, in the same slot, with 3.1 million (14.2%).
BBC1 initially struggled at 9pm with A Life of Grimegetting only 2.9 million (13.1%) but was given a boost 30-minutes later with Traffic Copsgaining 3.6 million (16.3%).
Five and BBC2 were absolutely neck and neck. Five's popular Houseand BBC2's quiz Mastermindboth managed 2.2 million (10.1%).
The situation amongst the broadcasters changed dramatically at 10pm with BBC1's news update on 4.6 million (25.3%).
ITV1's 30-minute Soccer Aidhad a tough time at 10pm with just 2.4 million (12.9%) a drop of 1.4 million viewers from Wednesday's show. C4's film My Best Friend's Weddingat 10pm amused 1.7 million (13.6%).
Over in multichannel homes, BBC4's new four-part series Paul Merton's Silent Clownsgot off to a fine start at 9pm with 463,000 (2.8%) over 60-minutes, making it the channel's fifth most watched programme so far this year. It peaked at 9.30pm with 526,000 (3.1%). BBC4's most popular show this year has been Kenneth Williams: Fantabulosa! with 866,000 (4.8%). It was also the channel's highest rated factual programme ever.
All-hours shares for Thursday 25 May 2006: BBC1 - 21.5%, ITV1 - 17.3%, C4 - 13.3%, BBC2 - 7.6%, Five - 5.6%, multichannel - 34.7%.