Its most recent figures show it placed £45m worth of media billings over the past year, up 12.5% year on year, with its retail clients doubling their use from £3.6m to £7.3m in the first half of 2009, while that for media owners leapt from £700k to £3.9m in the past year.

Nathan Beck, marketing director at Astus said: "With the downturn there's more pressure to get more value."

He added that outdoor is one of the biggest sectors, representing "30% of our billings but less than 10% of all money". He said this is because most site owners would prefer to have a poster displayed at a lower rate than leave it empty.

Jon Fennell director of printing services at rival Active International agreed. "Outdoor and cinema have had problems over the last six months - the numbers fell off the face of the planet. The good thing about that is from a trading perspective its very cheap to buy into."

However he was more cautious about the effects of recession boosting the use of trade credit for media buying. "Agencies are pushing trade as it has been recognised as an incentive for clients and being used as a spend mix," he said. "In recession the theory is barter performs, although this relies on clients keeping to the same spending patterns, which has not been the case. The result is barter has shown some growth although restricted, I would expect a better growth as we move out of recession and spending patterns settle down."

Trade credit works where a client sells an underperforming asset in return for trade credits which they can then subsequently mix into planned spends on other services through the trade credit company such as media campaigns.