http://www.bbc.co.uk/radio7/chaingang/

The nice people at Radio 4 have asked if I'd like to blog about a drama I'm producing for its digital sister-station, Radio 7. It's not something we've been asked to do before, so I'm guessing they, like me, are intrigued by the rather unusual nature of it.

The first thing to say about it is that it's short. Each episode is only a couple of minutes long, but it does mean that we can feature it on 7 in those gaps which would be filled with things like the shipping forecast on Radio 4. And we're hoping at that length it will go down well as a podcast too - we're adding in a bit of behind-the-scenes recording for that.

The other thing about it is that it isn't finished. This isn't just carelessness or brinkmanship on our part, but rather a deliberate ploy to engage our listeners in the process of storytelling. We've asked the award-winning short story writer Robert Shearman to write the first episode. That went out on Radio 7 on Saturday night at 1755, after which we've been asking people to head off to the website to send in their storylines for episode two. We've just been looking through those, and there's an amazing sea of creativity out there. Robert is at work now dramatising the best one which we'll record tomorrow and broadcast on Saturday. Hopefully it will all build to a fitting climax just before Christmas (we've some special plans for this), and we can all sit down with our turkey sandwiches on Boxing Day to enjoy the whole story together for the first time.

And what's the story about? Well, Brian and Susan Ferguson are enjoying a relaxed meal on their honeymoon. Brian heads off to pay the bill, and suddenly there's another woman at the table, issuing Susan with a dramatic warning. The stranger's name? Mrs Ferguson... the other Mrs Ferguson. There is a further twist, believe it or not in a two minute episode, but I'll leave that for you to hear - the whole thing will remain on iPlayer through the Autumn.

Now we know you're a clever lot on Radio 4, curious minds and all that, so it'd be great if we could persuade a few of you to defect for just a few minutes to join our Chain Gang. Listen out on Saturday night, and then and get writing some storylines for episode three...

Paul Arnold is a producer at BBC Radio 7

• Chain Gang is on Radio 7 at 1755 Saturdays. You can listen to the whole series until a week after the final transmission thanks to the wonders of the 'series catch-up trial'. You're invited to take a survey about series catch-up here.
• At the end of episode one you can hear a fascinating interview with the drama's cast about the bewildering process of recording a drama that hasn't been written yet.
• The previous series of Chain Gang won a Sony Radio Academy Award.
• There's a podcast to subscribe to too.
• Robert Shearman wrote 'Dalek', the episode of Doctor Who which brought the Daleks into the 21st century.

Yesterday something small but significant happened. Instead of disappearing from iPlayer when its 7 days were up, the first Episode of The Complete Smiley - The Spy Who Came in From the Cold stayed put. Which means that you can go back and listen to it before listening to Episode 2.

The unusual behaviour of The Spy is down to the "Series catch-up" feature of iPlayer - something that's been on offer for some TV series for a while, and which we're now starting to trial for radio programmes. Series catch-up means that all the episodes in a series are available until 7 days after the final episode is broadcast. So you don't have to worry about keeping up each week, but can catch up with the story so far at any point during the series.

There will be around 30 series in the trial between now and mid January, including quite a few from Radio 4. Most of the le Carré season will be included as well as an exciting Dickens serialisation and a complete series of Behind Closed Doors later in the year.

The reason that we're only offering a limited number of series is because this is a trial. The BBC already has permission from the BBC Trust, who regulate what we do, to offer TV programmes with series catch-up, but we don't yet have permission for radio. We're running the trial to find out how useful or interesting people think this is, and to establish what it would mean to offer it more widely. If all goes well we'll then use the information from the trial to ask for permission to offer series catch-up as a permanent feature.

I realise the BBC's internal processes may sometimes seem a touch bureaucratic, but it's important that we find out how popular or useful a new feature might be, how much it might cost, and also what impact it might have on the wider industry, before we decide whether to launch it. This particular trial is limited to 30 series, and we've picked them from across networks and genres to make sure we get a broad range of feedback (here's a list of the Radio 4 series included).

If you're interested in telling us what you think about series catch-up, as part of this trial, then you can take part in a survey that we're running. There's a link below, along with some more info. I'll also be happy to respond to any comments you post on this blog over the next couple of weeks.

Sarah Prag is Executive Producer, Audio Services at BBC Audio & Music Interactive

• A list of the Radio 4 programmes included in the trial.
• Troy's post from the BBC Internet blog announcing series catch-up for TV programmes last year.
• The series catch-up survey is now closed.
• Picture, Car rear view mirror, by net_efekt. Used under licence.