The World: UK media auditors establish foothold in the US.

With only 5 per cent of media spend audited, the US is out of step with the world, but that is about to change.

Given that nearly half of the world's advertising budgets are spent in the US, it seems surprising that it has taken so long for media auditors to set up shop in the country.

The stakes are huge - according to ZenithOptimedia, the total US advertising market was worth dollars 161.4 billion in 2004. In order to tap this massive and potentially lucrative market, over the past 18 months all of the big UK-based media auditing companies - Media Audits, Billetts and Fairbrother Lenz Eley - have established operations in the US.

There's no doubt that the US is way out of step with the rest of the world: media auditors have been offering their range of consultancy services in the UK for three decades, and claim now to be able to offer their services across every continent. But in the US, only 5 per cent of media spend is currently audited, compared with around 20 per cent in Europe and around 80 per cent in the UK.

However, the relatively recent separation of media from full service in the US, combined with demands for financial transparency and an increasing number of global media pitches, has meant that the US can no longer escape the attentions of the auditors.

They face a difficult task, though. With more than 250 separate television regions, the US media market is of an unrivalled complexity, a factor which has stymied the rise of the auditor in the past.

In order to check that airtime has been transmitted correctly, advertisers have had to depend on the agencies to self-report, or use the services of consultants to check campaign performance and verify invoices. In the past, this wasn't a problem - there exists in the US a closer and more trusting relationship between clients, agencies and media owners than has ever existed in the UK.