Image caption The most recent series of Strictly Come Dancing was Goodman's last as a judge

Len Goodman is expected to cause a spike in electricity demand as viewers bid farewell to the Strictly Come Dancing head judge, according to the National Grid.

BBC One will show a special programme, Strictly Len Goodman, on Friday.

The National Grid said the show would drive the biggest festive "TV pickup" - a sudden surge in electricity demand.

The spike is largely down to viewers turning on lights and boiling their kettles straight after the programme.

There is also a surge in the number of people going to the bathroom, which leads to a spike in the use of water companies' pumps, which draw electricity.

Image caption The Great British Bake Off Christmas special is also expected to create high demand

The Great British Bake Off, the Strictly Christmas special and Call the Midwife are also expected to create high demand over the Christmas period.

But TV surges create less demand now than they did 20 years ago because more people use catch-up services to watch TV and do not all see a programme live.

Jeremy Caplin, forecasting manager at the National Grid, told The Guardian that predicting electricity surges was determined simply by "picking up the Radio Times and seeing what people are interested in".

He added: "It is definitely art rather than science. Every morning somebody will go through the previous day and fill in the database to see what programme had a pickup. We can use that history to predict what will happen going forward."

The biggest Christmas Day TV pick-up of all time occurred in 1996, after a festive special of Only Fools and Horses.

However, the biggest surge in electricity demand on Christmas Day comes not from watching TV, but cooking. The National Grid said the biggest demand is in the early afternoon as turkeys are roasted.

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