“Have you got what it takes,” asks the online invitation, “to help record a new version of the Blue Peter theme tune?” Within six hours of its appearance on the internet, 3,000 children aged from 7 to 15 had replied in the affirmative. And as Blue Peter’s editor Richard Marson points out, this is an impressive response, given that the complex form would have taken about half an hour to fill in.

Anyone can apply, provided an adult sponsors the application. Blue Peter is looking for a 40-strong band, half of whom will be competent instrumentalists, and the other half enthusiasts with no prior musical training. There will be three regional auditions, followed by a three-day residential camp for the winners, who will then join the BBC Philharmonic to record the finished work on April 9. They will perform a longer version at the annual Blue Peter Prom at the Royal Albert Hall. The piece itself will be written by Murray Gold - a prolific film composer who is currently at work on Dr Who.

An extraordinary venture? No more so than the storytellers’ competition, which Blue Peter ran last year. They asked seven top children’s authors to start a story which entrants had to finish, and got 33,000 entries. “And the results were amazing,” says Richard. “The best ended up in a Penguin children’s book. That was a life-changing prize.”

This new competition arose out of a conversation he had with the manager of the BBC Philharmonic a year ago. “He asked what we could do on Blue Peter to make classical music, and orchestral music in particular, more accessible to children. I said that was a tough question, but let me think.

We were already doing the Blue Peter Prom, but - although it sells out - that is only a concert, with no active participation by children. And given that the underpinning of Blue Peter is all about active participation - not just being a couch potato - that seemed a question worth asking.”

The answer surfaced quickly, as did several other decisions. They would do it online, since most of their target audience are now linked up, and there would, as Richard puts it, be “no cruelty TV, which is creeping into children’s programmes now”.

He was determined that anyone who auditioned would walk away having had a fun day, even if they didn’t get any further. “Children are incredibly motivated by fairness, which is why they respond so well to our Blue Peter appeals. We must always work with that sense of fairness.”

The decision to invite Murray Gold to be the composer was an easy one, says Richard. “I’ve always admired his music, and the way it always makes you feel happy. And his thoughts about the theme tallied exactly with mine - which is that as it’s a hornpipe, it has to be developed in that spirit.”

The theme tune, says Gold, is going to be very percussive. “And in every child there’s an ability for this, which can be unlocked. Even if they are supposedly ‘tone-deaf’ children, they will still be able to do something worthwhile here. To create a basis for them to work on, I decided to mess around with things in the house - saucepans, a sock full of money, a brush and a shoe, even a plastic bag, which gave a really nice snapping sound when you tugged it. I just picked up bits and pieces, and then recorded it all electronically. It only needs a little exposure to making music to counteract the feeling of musical inferiority which many children have.

They won’t come out of this project amazing musicians, but they will come out having a different sense of what music is, and how it’s made.”

He has the same view about composition. “A child or an adult may say, ‘I couldn’t possibly compose,’ and you say, ‘Imagine you’re in a darkened room, and there’s silence, now I just want you to disturb that silence.’

And they’ll say, ‘How?’ and you say, ‘It’s a high note’ - ‘Is it stringy, or is it brass?’ and they suddenly realise they’ve been hoodwinked into composing.”

The lucky 40 in this competition will get to sit beside the players of the BBC Philharmonic, and will literally co-create the new version of Blue Peter’s theme tune “Barnacle Bill”, which will henceforth introduce the show.

* The closing date for entries to Blue Peter Music Makers is February 3.

Full details, previous theme tunes and an entry form can be found on www.bbc.co.uknewtalentmusicmakers