"In an early draft, Sarah fought off Mrs Wormwood's secretary with a gas capsule that made the secretary's nose turn green. But I didn't laugh. I thought 'Actually that's too silly.'"

Says Russell: " I make a career out of writing first episodes that then get commissioned. I know how to make them work. It's not scary; it's more exciting than anything else. It's about creating the tone. The Sarah Jane Adventures is slightly unusual in that it was commissioned before we'd written the script. If we'd written a load of rubbish, they'd have still had to make it!

Julie asked the the other day "How does writing for children differ from writing from writing for adults?" and I said "I'm not sure I can answer that", because it's on instinct. Fandom is obsessed with rules - all those rules of the past that I've read a million articles about, like you must always split up the Doctor and his companion, or you must use the sonic screwdriver in this way... well, we don't have rules like that. You might say that you do interviews sometimes, just as something to say, but that's rubbish. Writing with Gareth helped me hone those instincts into deliberate descisions, like putting in more gags, having a Tomorrow People-style computer in Sarah's attic, and having her drive a bus through a wall!

I love the fact that Lis doesn't play Sarah as all nice, like your favourite aunty. You know how spiky Sarah can be? It's how you would be if you'd spent your life in outer space, and now had to live as a neighbour to ordinary people. You would be the local mad woman, and she does play it like that sometimes - brittle and hard. I'm proud of that. In the last scene, you're really,really happy for her. It's lovely."