Broadband video catch-up services such as the BBC iPlayer are not cannibalising traditional TV viewing despite their much-hyped popularity, according to a report.

Meanwhile, commercial broadcasters are still struggling to generate revenues from these fledgling web offerings.

TV marketing body Thinkbox said that broadband TV services - such as 4oD, the iPlayer, ITV.com, the Sky Player and Demand Five - "seems to be incremental" to the traditional broadcast TV that people watched in the first six months of the year.

UK viewers watched an average of 3.77 hours of broadcast TV a day in the first half of the year, a 2% increase on the five-year average for the period, according to figures compiled by Thinkbox from ratings body Barb.

"That both broadcast and online TV platforms are growing simultaneously underlines how they fulfil different needs for viewers and that they can co-exist and indeed promote each other," said Thinkbox.

However, analysts argue that the broadband TV market is so small for these online ventures that the true impact cannot yet be known.

"These [online] services are not cannibalising traditional TV viewing," said Vincent Letang, an analyst at Screen Digest.

"First of all, in terms of the amount of money spent by advertisers, it is so small that it doesn't divert from broadcast TV money. The other reason is that in terms of the time spent using online TV services, it is actually very small," he added.

Despite the bear market for advertiser-funded media businesses generally, Thinkbox also said that commercial broadcast TV had a "record breaking" first six months of the year.

Total commercial impacts - the viewing of one ad, one time, by one person - was up 6% year-on-year.

And commercial broadcast viewing is "performing very strongly", up 4% on the same period last year, fuelled by factors including poor weather and the increase in digital TV penetration.

"This is a shaft of very bright light that cuts through any economic gloom," said Tess Alps, chief executive of Thinkbox.

"Advertisers should be taking advantage of a medium that offers proven effectiveness, increasing value and is growing," Alps added.

However, the outlook for UK TV advertising revenue for the second half of 2008 is less rosy, with market leader ITV last week predicting it was heading for a 20% year-on-year dip in September.

"There is an apparent paradox or dilemma around how audiences can be up and ad revenues down, but one reason that explains it is because demand for TV advertising is flat," said Letang.

"This means there has been an increase in the supply of ads in the market and that means prices dropping. You could say that eyeballs have never been cheaper in the last 20 years," he added.

Letang said that while this might seem like a situation in which advertisers might look to spend more to take advantage of bargain prices, many are in fact actually cutting spending because they can reach the same audience numbers for less money.

"Clients are looking at cutting costs, not expanding in this market," he added. "So it is actually not that great news that commercial impacts are up as this means that prices are down."

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