STV has been rapped over the knuckles by television watchdog, Ofcom, for a “serious” breach of broadcasting rules after it repeatedly showed too many station promotional messages.

The Scotsman has reported that the channel broke strict broadcasting regulations when it exceeded the time limit for advertising breaks on 85 occasions during a 14-month period.

According to the report, this was the third time in under two years that the broadcaster had been in breach of the three-minute, 50 seconds limit, with Ofcom claiming that staff had not been adequately trained.

STV reported itself to the regulator, but also claimed that its dispute with ITV had been to blame due to the sponsorship of programmes, but Ofcom said that it was still STV's responsibility to ensure that rules were obeyed.

Ofcom is quoted as saying: “In this case, STV had filled the gaps in its centre break schedules, occurring when ITV1 entered into sponsorship arrangements and broadcast sponsorship credits and STV did not, with trailers and station promotions.

“This caused the durations of the centre breaks on STV to breach rule 14 of the Code on the Scheduling of Television Advertising [Costa] on 85 occasions.

“The total number of breaches, when considered together with the significant period of time over which they occurred, indicated to Ofcom a serious compliance failing.

“Moreover, Ofcom was concerned that an incorrect remedy had been applied when the alignment issue was first identified, and continued to be applied for some considerable time.”

In its response, STV said it had investigated and had found the incidents were caused “inadvertently” because of the change to sponsorship arrangements in January 2010.

Staff had been given refresher training and the channel had taken steps to ensure sponsorship slots were carried on ITV1 shows.

The broadcaster also said because “only station promotion material was used to fill the sponsorship credit gaps, none of the 85 instances contained any additional commercial content, and the commercial minutage that it transmitted across each hour and each day remained compliant with Costa”.

An STV spokeswoman said: “We accept Ofcom’s ruling on what is acknowledged as a very complex issue which STV spotted and flagged to the regulator.

“At no point did STV transmit more than the permitted level of commercials. STV has a rigorous and ongoing training programme for staff.”