The news industry won't survive if self-censorship gains a foothold

No one likes us, we don't care" is a chant invented by supporters of Millwall Football Club after criticism by reporters. Today, it could apply equally to journalists. Jobs are disappearing, titles are closing and, as if the frozen blast of economic reality were not chilling enough, the law is refrigerating the atmosphere even further.

Mr Justice Eady's interpretation of the appropriate balance between privacy and free speech has made privacy law threatening to investigative journalism. Conditional fee agreements, super-injunctions and libel tourism have made English courts additionally attractive to litigants with secrets to hide. External threats to honest, fact-based reporting are plentiful, so it is additionally dispiriting to find journalists flirting with self-censorship. Following the leak of emails from the University of East Anglia's Climatic Research Unit, flirtation descended into heavy petting.

In several newsrooms, journalists expressed fears that exposing the failings of eminent climate change researchers might damage the planet. Environmental campaigners insisted that it would. Concerned and conflicted, editors came under pressure to self-censor.

History, which every journalist should study, offers clear examples of the damage this egregious enemy of integrity can inflict. Among the most instructive is the betrayal of the 1914-18 front generation by editors and correspondents who knew the blood-soaked, muddy, rat-infested truth about the trenches but suppressed it in the name of patriotism.

The wartime governments of Herbert Asquith and David Lloyd George had censorship tools, notably the Official Secrets Act and the Defence of the Realm Act, but they relied more on newspapers' willingness to censor themselves. This they did with jingoistic zeal. "Every day I realise more deeply the colossal task before us," wrote Herbert Reuter of Reuters, "and the necessity of sparing no sacrifice to succeed where failure spells ruin to three empires, and will involve the unspeakable blight of German military tyranny over the whole continent."

If that betrays determination to encourage men to volunteer for the horrors of the Western Front, C.P. Scott, the owner-editor of The Guardian, was at least as keen to keep them fighting. In 1915, Scott displayed his disregard for evidence in a letter to a colleague. "A wounded man - an educated corporal - just back from Loos sends a letter to us, too damaging for publication, from which it appears that in that engagement we shelled our own men," wrote the man who is now remembered for observing that: "Comment is free. Facts are sacred."

Late in the war, Lloyd George told Scott that journalists could be relied upon to self-censor. "I listened last night at a dinner given to (The Daily Telegraph's war correspondent) on his return from the front," said the Prime Minister, "to the most impressive description from him of what the war in the West really means ... Even an audience of hardened politicians and journalists was strongly affected. If people really knew, the war would be stopped tomorrow. But of course they can't know. The correspondents don't write and the censorship would not pass the truth."

Similar eagerness to support a dominant consensus corrupted coverage of appeasement in the 1930s. The Times and the Daily Mail worked particularly hard to spin a myth that Hitler was a man with whom Britain could do business. Others, including The Guardian, were only fractionally less culpable.

Today's reporters, tasked with scrutinising issues as defining as climate change, need to remember these examples of the harm journalism can do when it abdicates its duty to hold power to account. Championing the opinions of the powerful was pathetic when the powerful disagreed with each other. Now, as politics converges on the centre ground and personality replaces ideology as a criterion for leadership, the duty to question everything grows in importance.

Even the best journalists are vulnerable. BBC correspondents self-censored when they underplayed the extent of Euro-scepticism beyond the House of Commons. Conscience-stricken political correspondents spent much of 2009 regretting that they did not write what they knew about MPs' expenses long before The Daily Telegraph revealed proof of wrongdoing.

In a leader on 10 December, this magazine argued "if climate research is seen as 'tribal' and unable to bear scrutiny, the whole scientific edifice is weakened". It concluded: "Science must be tested. It is the only way knowledge advances." That excellent advice was offered in light of the controversy over the leaked emails from East Anglia. It applies as forcibly to journalism, which deserves to survive as a profession only if it performs its role as watchdog with renewed vigour and vigilance.