Geoff Elliott, editor of The News, Portsmouth, said companies and public authorities no longer felt any obligation to tell the truth unless it served their own interests.
"We know from Prince Andrew that the Palace has been lying for 20 years, and from the Lewinsky affair that President Clinton's aides had been lying constantly for seven months," he said.
"At local level it's the same. If they wanted a cynical press they couldn't have done a better job in creating one," he told the Guild's annual conference in Cambridge.
"Everyday we mount guard on the freedom of expression. We make others accountable to the public when they try to dodge their responsibilities."
Editors and journalists should not apologise for what they do as though it had no intrinsic worth, he said.
"Let us all withstand those who abuse journalists because we don't spin in the direction that serves their interests. It would be a corruption of our job to do their bidding, to tell it the way they want it to be told."
Mr Elliott renewed the Guild's call for a Freedom of Information Act. In 1996 Tony Blair said a Freedom of Information Act was "absolutely fundamental to how we see politics developing in this country", Mr Elliott said.
"The measure has been put into the long grass where some ministers are inclined to keep it. The worry is that we have a government like the others, one that is getting used to hiding away its business in secrecy and spinning a web of deceit around what it is really doing."
Ian Hargreaves, professor of journalism at Cardiff University, commented last night: "I doubt that politicians or those in public life lie more than they used to, but Geoff Elliott has got a point that the increasing professionalisation of public relations presents an ever bigger challenge to journalists.
"Over the last few days we've seen how Ron Davies ... seems to have found it extremely difficult, indeed impossible, to give a straight answer to a straight question about anything that has gone on."
Mr Hargreaves also urged political journalists to resist being spun. "It's essential that journalists never feel part of a club or, if they are required to be part of a club, they must be an extremely disruptive member of that club. I do think it's possible for individual journalists to resist being spun, but not enough do."Reuse content