ITV overcharged X Factor viewers to the tune of £200,000 in an interactive vote blunder, the broadcaster admitted on Wednesday.

The error – affecting 1.3 million votes – occurred during every live show in the last series.

Viewers who voted by pressing the red button on their remote controls should have been charged 35p. Instead the calls cost 50p.

The blunder came to light during a company audit. ITV blamed a data inputting error and pledged to repay the money, taken during shows broadcast between October 14 and December 16 last year.

It will also donate £200,000 to Childline.

A spokesperson said: “We very much regret that a mistake was made in the red button payment systems during the last series of X Factor and we apologise to all those viewers affected.

“ITV operates a robust audit system which closely monitors interactive revenues and this system picked up the incorrect pricing at the first available opportunity.

“This was an isolated incident of human error and since this incident ITV has undertaken a thorough review of the operation of its interactive services and systems.”

The broadcaster also under-charged viewers who used the red button to vote in a competition to win a holiday. Votes should have cost £1, but entrants were charged just 35p. ITV has decided to write off the cost.

Anyone wishing to claim back their 15p overpayment can contact ITV on the freephone number 08000 63 62 63 or through www.itv.com/help. They must provide a telephone bill as proof of entry.