Channel 4 is to face investigation from Ofcom due to an extended outage of its subtitle services last year.

It faced a number of major problems in September 2021 caused by issues at the centre which handles its playout services.

A fire suppression system was triggered at the broadcast centre of Red Bee Media, severely damaging a large number of hard disks in a variety of systems

It's subtitling, signing and audio descriptions were among those affected – prompting the National Deaf Children’s Society (NDCS) to call for regulatory action to be taken.

Ofcom said Channel 4 had fallen short of its subtitling quota on Freesat, a subscription-free satellite TV service offering more than 170 TV and radio channels.

A statement from the media watchdog said: “We have found that Channel 4 managed to meet the statutory requirement to subtitle 90% of its programme hours over 2021 on most programmes. It also met its requirements for audio description and signing.

“However, Channel 4 fell short of its subtitling quota on Freesat, a satellite TV platform used by around two million UK homes.”

Ofcom “remains very concerned” about the incident, which it said resulted in a “lengthy outage to Channel 4’s access services provision and also wider disruption to its general broadcasts on all platforms”.

It added: “So, as well as investigating Channel 4, Ofcom is undertaking a review of the transmission arrangements and back-up facilities the affected broadcasters had in place at the time of the outage, and what changes they have made or planned as a result.”