The government was forced to clarify that it will play no role in judging any self-regulatory press body after a senior civil service press officer said the new Independent Press Standards Organisation (Ipso) was the "only show in town" – and said the Guardian should not be allowed to join.

A spokesperson for the culture department said it was up to the press to decide how to develop the work of the new body that has been established by some national newspapers, adding it was "not for the government to judge" any proposed self-regulator.

The culture department's intervention came after Richard Caseby, the former managing editor of the Sun who is now director of communications at the Department for Work and Pensions, praised the proposed new self-regulatory body, which is supported by his former employer.

In an article for the Press Gazette, Caseby wrote: "Ipso is now the only show in town and looking more solid by the day under the recently announced stewardship of Sir Alan Moses, a retired court of appeal judge." Caseby also suggested that the Guardian should be "blackballed" by the new body on the grounds that it has published a number of inaccurate articles about the government's welfare reforms.

He cited an article last month in which the Guardian columnist Polly Toynbee said that people should "forget civil service factual information" on the grounds that the work and pensions secretary, Iain Duncan Smith, "has just hired a Murdoch managing editor". Toynbee also wrote that the personal indendence payments (PIP) replaced the disability living allowance (DLA), which Duncan Smith cut by 20%. She also wrote that Atos, the firm contracted to run PIP. has "walked away".

Caseby pointed out that the Guardian apologised for any misunderstanding after making clear that he had not been hired by Duncan Smith and that he works as a civil servant "in a thoroughly honest, diligent and professional manner". It also amended the article to make clear that Atos's contract to deliver PIP continues. It is leaving a separate contract to administer work capability assessments (WCAs). The Guardian also amended the article to make clear that DLA is available for children up to the age of sixteen.

The DWP communications director also cited a Guardian article earlier this month which said that the number of zero hours contracts has reached 1.4m. The article was amended to make clear that the ONS figures cited by the Guardian related to the number of contracts that do not guarantee a minimum number of hours. Caseby also cited a Guardian article earlier this month which said that the DWP is the "government's worst offender when it comes to providing a living wage". The article was later amended to make clear that nine government departments and agencies had been unable to provide figures for the survey cited by the Guardian.

Caseby said the articles showed that the Guardian was not fit to sit on Ipso. He wrote: "Should the new Ipso members accept Mr [Alan] Rusbridger [editor in chief of Guardian News and Media] as a Johnny-come-lately? No, rather he should be blackballed. Sorry, but the Guardian isn't fit to become a member of Ipso until it starts valuing accuracy."

"In the end, of course, it's Ipso's decision. But should the new standards body be so gracious as to invite him in, I guess I'll be waiting to lodge the first complaint."

Ipso is backed by the Telegraph and Mail titles. But the Guardian, the Independent and the FT are not supporting the body.

A Cabinet Office source added that Alex Aiken, the executive director for government communications, had not approved Caseby's article. A source said: "It was not authorised by Alex Aiken. It was just a blog by Mr Caseby."

But the source indicated that no action was likely to be taken against Caseby as he is a senior figure who should be free to decide how to respond to press reports about his department.

But Bernard Jenkin, the Tory chairman of the commons public administration committee which oversees the civil service, said: "There was a time when such passionate support for the government's position from a professional civil servant would have raised many eyebrows. But there appears to be a new definition of impartiality which permits this kind of expression. The question is what do we mean by impartiality because there is rather less consensus about this than there was."A Labour source said: "It is absolutely not appropriate for politicians or civil servants to make a judgment call on the new system of press self regulation.It is still in the process of being formed."