Director General Mark Thompson said the idea, known as Project Barcelona, was the “digital equivalent” of buying a programme on DVD.

He said in a speech to the Royal Television Society that the success of their iPlayer on demand service hadn’t stopped the fact that “a large proportion of what the BBC makes and broadcasts is never seen or heard of again”.

He said: “In addition to the existing iPlayer window, another download-to-own window would open soon after transmission – so that if you wanted to purchase a digital copy of a programme to own and keep, you could pay what would generally be a relatively modest charge for doing so.”

The price is rumoured to be around £2 per show, which could be kept forever.

But Thompson insisted that it wouldn’t be a “second licence fee by stealth” and added that other providers would be able to sell the content too.

When the new service is launched rivals such as Apple’s iTunes and DVD makers could be hit.

Media commentator Steve Hewlett said: “Other broadcasters could be concerned about the service’s impact.

“When it launched, iPlayer was extremely disruptive to emerging paid-for content models because it was free at the point of use. People will be asking whether Project Barcelona will have a similar effect on the market.”