The channels join BBC Three and BBC News which are already simulcast, and can be watched online via their channel sites on bbc.co.uk through a wide range of internet enabled devices.

They can also be watched through BBC iPlayer. BBC Vision director Jana Bennett said, "The launch of three more BBC Television channels further fulfils the BBC's commitment to increasing the accessibility of our content to licence fee payers.

"Although still a relatively new phenomenon, watching programmes online is growing; now through simulcasting our channels, viewers can find and watch programmes as they are broadcast as well as having the option of catching up with them later."

Recent research by Ofcom (The Communications Market 2008, August) suggests that consumers of all ages are showing a growing interest in accessing audio-visual content online, with 17 per cent of those with broadband watching TV on the internet, up by eight percentage points on 2006.

This trend is particularly apparent in younger people who tend to watch less television.

26 per cent of those aged between 15 and 24 claimed they used the internet for "watching TV programmes" – up by 16 percentage points in 12 months.

BBC controller of multiplatform and portfolio Simon Nelson said, "Simulcasting online is another step in making our channels true multiplatform brands accessible to audiences wherever they want and providing lots of opportunities to let them discover a wealth of related content through the channel and programme sites."

Simulcasting BBC Four, CBBC and CBeebies is being launched as part of a 12-month evaluation period. Video on the channel sites is GEOIP restricted, so can't be viewed from outside the UK.