Craig Johnson (pictured), AGB Nielsen’s managing director in Turkey, told Research that some families said they were offered up to 300 Lira a month (approximately £130 ) to watch certain programmes and switch off during advert breaks.

He said: “We were alerted by one of our households on 10 April that they had been contacted by a third party. We don’t know who this third party is and we’re not going to speculate. We’re going through the due legal process to identify them.”

Johnson said 41 households had now been in touch to say they were contacted. Reports in the Turkish press putting the figure as high as 200 were exaggerated, he said.

“Households that have been contacted have been taken off our directory,” said Johnson. “That is 41 in total out of a panel of 2,500. Not all have confirmed tampering but we have an internal process that we run to detect unusual changes in viewing habits.”

The firm, along with TÍAK, has asked a prosecutor in Ízmir, the town where the majority of respondents were contacted, to investigate the matter and identify those responsible.

Johnson added that reports that TÍAK is planning not to renew AGB Nielsen’s measurement contract, which it has held for 20 years, were inaccurate.