Proposals by MI5 and MI6 to extend courtroom secrecy to civil trials would unfairly restrict the right of the media to act as the "eyes and ears" of the public, the supreme court heard today.

The media's role is of particular importance in cases where the two agencies are facing allegations of complicity in torture, Lord Lester QC, representing the Guardian, the Times and the BBC told the court.

He said the proposals would not only interfere with the common law and European convention right to freedom of expression, but would undermine "the freedom of the press in acting as eyes and ears of the public as reporters of matters of legitimate concern". The secret court judgments that would follow would exclude media reporting "for all time", he added.

The agencies, along with the Home Office, the Foreign Office and the attorney general, are arguing that the so-called special advocate procedure could be extended to the civil courts.

The procedure is used in control order cases and some terrorism-related immigration tribunals. Sensitive material is disclosed to vetted barristers who can then make submissions to the courts but not discuss with their clients what they have seen.

The case arises out of high court proceedings brought by former Guantánamo inmates who sued the UK government for damages. Classified documents disclosed during those proceedings revealed the depth of British involvement in the post-9/11 rendition programme, and showed that ministers, including Tony Blair, decided rendition to Guantánamo was their "preferred option" despite being warned that people sent there were tortured.

The Guantánamo cases have been settled, with the government paying undisclosed compensation, but a number of other men alleging UK complicity in their torture in Pakistan and Bangladesh are also suing.

The hearing continues.