The Liberal Democrats have demanded that Lord Mandelson let MPs know what is being decided under the Anti-Counterfeiting Trade Agreement (Acta).

The negotiations currently under way over the proposed plurilateral international agreement on intellectual property rights have been kept firmly behind closed doors; even opposition MPs are unaware of developments.

This has caused huge concern among consumer and civil liberties groups because of the implications it could have for UK legislation; including copyright laws and enforcement procedures if these are breached in the digital environment.

Jill Johnstone, director of Consumer Focus, said: “The Acta negotiations have so far been conducted in secret, as if it was simply a bilateral trade agreement.

"But the decisions made by Acta could have a direct impact on the copyright laws of member countries so it is vital that the draft negotiating text is made public.

“The UK Government should press for open and transparent negotiations involving all the relevant stakeholders. It would also ease some of the suspicion surrounding this agreement if the negotiating parties disclosed the type of copyright violations it will cover.”

Now the Lib Dems have also baulked at the secrecy surrounding Acta and Don Foster, shadow culture secretary has written to Lord Mandelson.

“He must act to release the details of this agreement as soon as possible. Legislation on internet piracy is currently being debated in Parliament.

"Given that this agreement (Acta) could override any decisions taken over the next few months, MPs have a right to know what is being decided,” he said.

Currently discussions are taking place in Mexico until 29 January. Jérémie Zimmermann of La Quadrature du Net said "There will be other rounds. Probably two or three this year. They intend to finish in 2010."

The civil liberties group is also urging people to demand transparency. Mr Zimmermann said: "Unelected negotiators - carrying out the orders of the entertainment industries - are attacking the very essence of the internet.

"More than 80 non-governmental organisations from all over the world (including Consumers International, Reporters without Borders, the Free Software Foundation and the Electronic Frontier Foundation) already signed an open letter strongly opposing Acta.

"La Quadrature du Net calls on every citizen to participate in raising awareness on the dangers of Acta and to expose its negotiators in order to make them accountable. A dedicated participative campaign page is provided for this purpose."