The BBC's archive is a phenomenal resource of over 4 million items. It can allow us to experience and understand all sorts of cultural, social and economic aspects of life in the UK from the 1950s onwards. You can see some examples of material from the BBC's archive online in the Archive collections. But sadly, as Andrew highlighted, we don't have recordings of many programmes that we have broadcast over the decades - and I wanted to share the reasons behind this, and ask for a bit of help.

That lots of recordings were taped over reflects how we have thought differently about television over time. In its earliest days, television was not seen as something you might want to keep. It went out once, live, and that was that. It was simply not envisaged in those days that people might want to view those episodes again decades later, and even if they had, early recording techniques were very limited.

Even as recording technology became more available in the Fifties, other constraints mitigated against long-term collecting of programmes. Concerned about the implications of recording and repeating television on their employment prospects, actors' unions and others with an interest in programme-making sought to limit the rights of broadcasters to re-screen programmes. Meagre prospects for re-screening, along with the high costs of recording tape, meant much that much television of that era still wasn't kept.
In the following decades, the BBC, like every other broadcaster, still couldn't record everything. Tape recording was very expensive, so keeping recordings of shows was often a luxury, rather than a routine, and tape frequently had to be re-used and recorded over.

There was a real shift in thinking in the mid-1970s, when the BBC began to comprehend the longer-term value of what it created. At that time, BBC archivists and librarians began to exert more control over the management of its archive in an attempt to safeguard programmes for the future.

As Andrew says, the arrival of digital technology means there's no need to tape over anything, and nowadays, everything transmitted on national television and radio is recorded and kept. The main issue facing audio-visual archives now (and not just those of the BBC) is the long-term preservation of archive material, whether through digitising older recordings, or through maintaining appropriate storage conditions for increasingly fragile older material. Neither of these is cheap or easy. But we have to act now to make sure our archives survive so that future generations can enjoy them and learn from them too.

Amazingly, we do uncover items from time to time that we thought had been lost - with people finding old tapes and sending them in. I do wonder how many "lost" BBC recordings are sat in storage in people's houses.

So if you do happen to have an episode of Doctor Who from the 1960s some of which are missing, or Bob Dylan's 1963 acting debut in your attic, we would dearly love to hear from you...

Sarah Hayes is the Controller, Information and Archives.

Ed's note: If you'd like to find out more about the BBC's archives there's an interview with Adam Lee on the BBC Archive website where he answers various questions including "Why aren't there many recordings from the early days of television?" and "Once the technology was available, why weren't all programmes recorded?". (PM)