Up to 40,000 cable customers were left without a TV signal during Saturday night's X Factor final.
London receptionist Leona Lewis, 21, won The X Factor
Subscribers to NTL Telewest's TVDrive service were unable to watch any channel between 1430 and 2030 GMT.
The TVDrive, which is the cable operator's answer to Sky Plus, would also have failed to record shows like Planet Earth and Strictly Come Dancing.
"I am extremely sorry," said chief operating officer Neil Berkett, who called the incident "highly unusual".
"I realise that this will have caused huge disappointment," he continued. "I would like to offer my personal apologies for this."
About 1% of NTL Telewest customers subscribe to the TV Drive service. Many of them will have been able to watch terrestrial shows such as X Factor through their aerial.
The talent show's final gave ITV1 one of their biggest audiences of the year, as 10.4 million people tuned in to see 21-year-old Leona Lewis beat Ray Quinn.
But six million people deserted the channel after the programme, with the interactive widlife show Extinct only managing to secure an audience of 4.1 million.
The penultimate episode of Strictly Come Dancing was seen by 7.2 million people on BBC One.