Anti-spam experts have balked at the idea of the government forcing internet service providers (ISPs) to adopt anti-spam filtering technology.

At a public inquiry on spam held by the All Party Parliamentary Internet Group (APIG), anti-spam software specialists Brightmail, Clearswift and MessageLabs told the committee that, while such measures could help stem spam, the implications would be too onerous.

"If all ISPs did install filtering technology it would make email traffic more manageable, but if you do this what is the next step? You could end up with government deciding what messages we were getting," warned Gert Veendal, European director at Brightmail.

But the companies agreed that ISPs did have a duty of care towards their customers and could increase their efforts.

"More than 80 per cent of spam gets through because of open proxies, but ISPs have no incentive to close them," explained David Kehoe, vice president of marketing at MessageLabs.

A proxy is software that handles network communication and allows access to the internet. If misconfigured - called an open proxy - it can be hijacked and spammers could bounce their connections through the system. It became clear that policing any anti-spam policy and enforcing legislation are major hurdles.

In the UK, responsibility for enforcing spam laws will rest with bodies such as the Office of Fair Trading and the Office of the Information Commissioner.

But Liberal Democrat MP Richard Allan questioned whether the Information Commissioner had the resources to deal with enforcement.

Derek Wyatt, co-chairman of APIG, who warned that the US Can Spam law could lead to anarchy, said that it was not clear where any due legal process could take place. He believed the establishment of a new international body should be discussed.

Clive Gringras, a lawyer and chairman of the ISP Association's legal forum, said it was unclear whether extradition treaties could be invoked if UK courts wanted to prosecute people for breaching UK regulations.

But with so many questions unanswered, APIG is running another public inquiry on 10 July. The information from both inquiries, along with written submissions gathered by APIG, will be used in a report due in October.

This will outline the current position and future trends, and make recommendations to government, industry and consumers on how best to tackle spam.