A real Hoot

The only help he gets is from white boards with names or directions on, so that he can navigate a giant circle of bands, singers and guests.

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When the recording is over, Jools told me: "It's a bit like a swimming pool, you just throw yourself in and it's all right, really, once the water's OK and you start swimming, you keep the momentum going.

"You're trying to remember what you're playing on piano. When that finishes, you think, 'What happens now? That's why they've got a board, so I can remember where I've got to go to for the next bit."

The aim is to film it without any breaks or stops and, aside from a couple of brief moments when production requests a pause which is necessary, filming is nonstop. Jools explained: "You want the energy to keep going. So if we record it in one then it's like real. It was all just, bang, bang, bang.