The Government's ban on pressure groups using television advertising to promote their cause is under pressure after a High Court challenge this week.
The animal rights group Animal Defenders International is seeking to overturn a provision in the Communications Act 2003 that prevented it running an ad opposing the use of monkeys and apes in circuses and in advertising. The ad, which used the strapline "my mate's a primate", was banned by the Broadcast Advertising Clearance Centre on the grounds that "political advertising" is outlawed by the Act.
ADI is being backed by groups such as Amnesty International and the RSPCA, which argue the ban is "incompatible" with their right to freedom of expression under the European Convention on Human Rights.
If ADI wins the case, it could open the floodgates for pressure groups to run high-profile TV and radio campaigns.
Last year, Make Poverty History's TV ad was banned by Ofcom for having a political message.
Lawyers for ADI pointed out that wealthy organisations such as oil companies could use TV ads to promote their environmental credentials to the public, while the Act denied green campaigners "30 seconds" to respond in the media.
Michael Fordham, for ADI, accepted that restrictions should be applied to party political advertising. However, he said, the ban went far beyond what could be regarded as political advertising and could not be upheld as necessary in a democratic society.
The Government has argued that campaigning organisations are free to advertise in non-broadcast media, including the cinema, the internet, newspapers, magazines and billboards. Fordham called this "half an answer" and insisted it ignored the unfair treatment of groups such as ADI.
Lawyers for the Government are fighting the challenge in a hearing expected to last three days.
A written submission on behalf of Tessa Jowell, the culture secretary, said the British courts did not necessarily have to follow rulings from the European Court of Human Rights.
It added that she regarded a 2002 ruling, in which the European court overturned a ban on a Swiss pressure group's campaign on pig-rearing practices, as "unclear and unpersuasive".
The High Court's judgment is due in the autumn.