Hopes that TV advertising revenue would bounce back from a dire September are fading, with media buying agency sources predicting that ITV1 could face a second consecutive month of double-digit percentage year-on-year decline in October.

ITV1, the largest commercial channel in the UK and a bellwether for the health of the TV ad industry, could be down by as much as 16% year-on-year in October, in a worst-case scenario according to media buying sources.

However, if ITV1 is able to snare a significant amount of "late money" - advertising spend that comes in after the advanced booking deadline - it could limit the damage to a drop of about 10% year on year.

Advertising across ITV's portfolio of channels - including ITV2, ITV3 and ITV4 - could also help limit the broadcaster's month-on-month ad revenue drop to about 10% in October.

The total UK TV ad market is predicted to be down about 10% in October, with some media buying sources expecting a drop of as much as 12% compared with the same month last year.

Ad revenue at Channel 4's flagship network could also be down by 10% or more year on year in October.

But ad revenue from the broadcaster's family of digital channels, including E4 and More4, is likely to restrict Channel 4's overall year-on-year decline to less than 10%.

Sky Media, which sells ad airtime for BSkyB's channels and a number of other multichannel operators, looks set to be down around 14% year on year.

Channel Five is likely to be down between 6% and 10% year on year. Across its portfolio of channels, including Fiver and Five US, the RTL-owned broadcaster may end up being down about 6% in October.

ITV, which is already set to be down close to 20% in September, has partly blamed the Rugby World Cup in 2007 for skewing the year-on-year comparison for next month.

However, October looks set to be similarly skewed for ITV's year-on-year ad revenue comparision, as the Rubgy World Cup, which saw England reach the final against South Africa, finished on Saturday October 20 last year and the tense climax of Lewis Hamilton's first formula one title race the following day.

This sporting double whammy gave ITV its single biggest grossing weekend of the year in 2007, hauling in as much as an extra £16m in ad revenue.

Some media buying sources had optimistically hoped that the October British TV market might stabilise at a less drastic 7% year-on-year decline in overall ad revenue, compared with September, with ITV1 posting a dip of less than 10%.

However, a consensus of figures from media buying agency sources makes this forecast seem increasingly unlikely.

· To contact the MediaGuardian news desk email editor@mediatheguardian.com or phone 020 7239 9857. For all other inquiries please call the main Guardian switchboard on 020 7278 2332.

· If you are writing a comment for publication, please mark clearly "for publication".