BBC director of new media and technology Ashley Highfield, who topped Revolution's first Power 50 this month, said the pilot with 5,000 BBC users began in September and would run until the end of the year.
The trial will help the Beeb to test its success in addressing a series of technical obstacles before it can offer full access to its programming from the past seven days over the web.
These include digital rights management and keeping the content free for UK licence-fee payers. However, the trial will also provide insight into which kinds of content will prove most popular on the web and form the foundation for the provisionally titled MyBBCPlayer, which is planned for launch next year.
MyBBCPlayer will aim to combine the seven-day 'catch-up' service of the iMP with live-streamed BBC TV channels and content from the archives.
Highfield said: "This trial builds on all of those technical issues to take them further - to make sure we have good digital rights management; that we can keep it within the UK; that we can use multicasting and peer-to-peer - but then it answers the really big question, which is 'does the audience want this?'."
See cover story, p30.