The commercial station’s all-day average audience has dropped by 12% in the past year – and its share is understood to be at its lowest ebb. STV’s audience has declined by more than twice the rate of ITV’s as the Scottish broadcaster moved to drop network programming.

The data shows that STV’s audience share was 16.9% for the first 34 weeks of this year compared to 19.1% over the same period in 2008 and 20.1% in 2006.

ITV1 which had a 17.3% share this year has for the first time in recent years overtaken STV’s audience share performance.

The figures add more weight to critics who say replacing network programmes with repeats, cheap imports and old movies is not working. But STV believes its audience share will improve as investment in Scottish programming makes its way on to the schedule.

STV does not have to pay for network shows it does not screen. That means a programme costing between £500,000 and £700,000 an hour would save STV £30,000 to £40,000.

ITV has attacked STV for failing to pay £15m in fees, plus other charges estimated at a further £7m for being part of the ITV network, dating back to 1999. STV has rebutted the allegation, and insists it remains committed to the network and is negotiating with ITV over the fees issue.

The one new network drama from ITV’s line-up which will make it on to the Scottish station this autumn is Murderland, which stars Scots actor Robbie Coltrane and is set in Scotland.

Yesterday STV replaced the new ITV series of Agatha Christie’s Marple with the seven-year-old surfer movie Blue Crush. Another of ITV’s roster of new autumn drama series, Blue Murder starring Caroline Quentin will be ditched for the cheaper Irish drama from RTE, Single-Handed.

One Scottish media expert said: “It is baffling that STV is continuing with this strategy, which is bound to affect advertising at a time when figures show their advertising revenues are dropping.

“It is not a strategy for a channel that aspires to be the main broadcaster in the country, and it is not offering people the quality of service they are entitled to expect.”

STV said 2008 audience figures were “flattered” by high audiences tuning into watch the European Football Championship.

A spokeswoman added: “STV is Scotland’s biggest media brand with more than three million viewers per week, and we remain Scotland’s most popular peak time broadcaster. We have recently launched a new, long-term programming strategy and are seeing early signs of success.

“In addition to network material, we’re commissioning more original productions, acquiring strong new series and are confident our schedule will become even stronger and richer over time.”

Concerns that Scots are switching off STV have been echoed in the latest audience figures for network dramas the Scottish broadcaster has decided not to show.

STV’s decision to axe crime drama The Fixer in favour of a repeat of Fitz, the 12-year-old American remake of the 1990s crime drama Cracker, proved a ratings disaster.

The Fixer broadcast at 9pm on Tuesday drew 3.8 million and 16.7% audience share on the ITV1 network while STV’s Fitz managed just 178,000 viewers and 9.4% on STV.

But STV’s move to replace a fresh episode of The Bill with the Scotland Goes To War documentary on Thursday proved a better move.

The Bill: Powerless shown at 9pm averaged 3.6 million and 15.1% on ITV1 while Scotland Goes to War on STV averaged 322,000 viewers and 16.3%.

The Bank Holiday ITV adaptation of Emily Bronte’s Wuthering Heights wooed four million and 19% on Sunday while the seven-year-old mini-series Sirens, starring Daniela Nardini, drew 366,000 and 19.8% for STV. The concluding part of both dramas on the Monday saw Wuthering Heights pulling four million and 18% while Sirens gained 404,000 viewers and 21.5%.