Channel 4 has written to Barb raising “serious concerns” after the audience measurement body misreported its ratings last month.

The commercial broadcaster is understood to have brought the issue, which also affected ITV1, to Barb’s attention last week after spotting a number of “anomalies” in its viewing figures.

A senior source indicated that C4 has written to the audience measurement organisation - which is funded by all of the UK’s major broadcasters - requesting a meeting to root out the issue and prevent it from happening again.

Barb is still investigating and has initially blamed an “error in audio referencing procedures”, meaning ratings for ITV1 and C4 shows were “misallocated” between 19 and 24 September.

The result is that in some cases viewing to ITV1 shows has been deducted and helped artificially boost C4 figures. The same has also occurred the other way around.

Commercial implications

The gaffe is “terribly rare” according to one industry source, who suggested that ITV and C4 could be “livid”, particularly as it may have had commercial implications in their dealings with advertisers.

The incorrect data has now been amended by Barb, meaning audience figures for some high-profile shows have been significantly altered.

The X Factor is one such example. The entertainment show originally recorded an overnight audience of 8.96m (33.6%) on ITV1 and ITV1 HD in figures released last Monday, but this has now grown to 9.84m (36.91%) under the revised data.

Some C4 shows, including 999: What’s Your Emergency and Grand Designs, have also experienced audience uplifts after the figures were corrected.

However, others have fallen, such as the 22 September episode of The Comedy World Cup, which dropped from 1.8m (7.9%) to 631k (2.76%) on the back of the gaffe.

“The Barb service is complex and covered by high levels of quality control, and there are procedures to mitigate against potential errors such as this one,” a spokeswoman for Barb said.

“Barb is awaiting a report from its research contractors into how these procedures seem to have failed in this instance.”

C4 and ITV declined to comment.