Young trees growing in the UK
George Monbiot chose to work for two nature charities under the agreement reached with Lord McAlpine. Photograph: Mar Photographics/Alamy

The columnist George Monbiot won’t easily forget the late Lord McAlpine.

After defaming McAlpine via Twitter in 2012, Monbiot publicly apologised and agreed to do charity work worth £25,000 over three years from March 2013.

That agreement is now discomforting the Guardian, which was not a party to it.

In a clear breach of editorial standards on conflicts of interest, Monbiot in some of his published Guardian pieces assisted two charities without disclosing to readers that he was under an obligation to work on the charities’ behalf.

“It is always necessary to declare an interest when the journalist is writing about something with which he or she has a significant connection,” say the Guardian’s guidelines. “This applies to both staff journalists and freelances.”

As journalists routinely remind governmental and corporate figures, disclosure matters when circumstances mean that a person can reasonably be regarded as having conflicting loyalties. In journalism, the impetus for managing conflicts properly is the same as in other fields. Mismanagement, especially a failure to disclose, can erode trust.

On seven occasions between May 2013 and December 2015, Monbiot’s Guardian work referred favourably to Trees for Life and its founder Alan Watson Featherstone, or to Widehorizons, an educational charity that gives children experiences of the natural environment.

Two references to Trees for Life were brief, made in passing, as was one to Widehorizons. Two to Widehorizons were central: in a column about education and in a video showing Monbiot introducing children to a seashore environment.

In another column, Monbiot declared an interest in Rewilding Britain, which he helped to found, but not Trees for Life. The seventh reference was published under Monbiot’s influence but not his name.

Last December, the Guardian published its alternative New Year’s honours list. Among 35 named individuals, including Angela Merkel, Barack Obama, Edward Snowden and Malala Yousafzai, was Alan Watson Featherstone.

Monbiot nominated him for his work to bring back lost Caledonian forest and the species that inhabited it.

Neither the sincerity of Monbiot’s nomination nor Featherstone’s merits are in question here. The point is Monbiot ought to have disclosed to the editors of the list his obligation to Trees for Life derived from the McAlpine agreement.

I learned of Monbiot’s arrangements with the two charities from a reader who sought an investigation and said he planned to write an article. Monbiot co­operated readily with my phone and email inquiries and acknowledged frankly his failing: “I did not pay sufficient attention to the guidelines and should have declared an interest.”

Initially, Monbiot was to help three charities but it was reduced to two. Monbiot, not McAlpine, chose Trees for Life ­ because he already knew Featherstone and his work. He selected Widehorizons from 130 charities which responded to his call­out on Twitter after publicising his agreement with McAlpine.

The Guardian guidelines say that a declaration should be made to a head of department or editor during the preparation of items. “Full transparency may mean that the declaration should appear in print and on the website.”

Monbiot told me he cannot be sure, and has no written record of it, but he thinks he recalls telling the names of the charities to two senior editors with whom he liaised at the Guardian. Both editors have since left the Guardian. I contacted them and both said they had known of the agreement but could not recall Monbiot having told them the names of the charities.

The editors who succeeded the pair during the remainder of the three­-year period told me that Monbiot had not disclosed the names to them.

Monbiot’s other work for the charities included lectures, teaching, advice and introductions. From the charities’ perspective, the mentions in the Guardian were not insignificant. Monbiot’s public profile was a large part of what made him valuable to them, and the leaders of both told me they were pleased and grateful for his involvement, which Monbiot and the charities say they intend to continue.

The venality which can characterise conflicts of interest cases is absent from this one. Readers were not misled in a material way. The choice of the charities was consistent with the environmental advocacy for which Monbiot is well known. This is relevant in assessing potential harm to trust.

Had Monbiot failed to disclose an agreement to assist, say, a big oil or coal company, the impact on readers’ trust in him, the Guardian’s trust in him, and perhaps readers’ trust in the Guardian, would have been justifiably severe.

The two lawyers who negotiated the agreement for McAlpine confirmed Monbiot’s statement that there was no formal agreement document. The charities said the same about their relationships with Monbiot. Nor was there a formula for valuing elements of Monbiot’s work so that progress towards the £25,000 total could be calculated.

The lawyers said they were satisfied with the workings of what they and Monbiot described as a gentlemen’s agreement. McAlpine, who died in 2014, was a fair man who had been impressed by Monbiot’s apology, said the senior lawyer, Andrew Reid of RMPI LLP.

No formal progress reports had been sought from Monbiot. ­ “We took him to be a man of honour,” Reid said.

Monbiot told me that not making a declaration “looks stupid in retrospect but, as far as I can recall, it just didn’t cross my mind”.

Referring to the column which gave Widehorizons prominence, he said that after seeing the charity’s work with children he was so enthused he just plunged into the article as he would any other.

“As far as I was concerned, the work I did for the charity was the teaching, and the article was work for the Guardian. This does not make it right, of course: as the editorial guidelines make clear, I should have declared the connection. But I had no intention to mislead anyone and no interest in doing so.”

The independence the Scott Trust grants to the readers’ editor to investigate and to publish has resulted in necessary disclosure. Disclosure notes will be added to each of the seven items for future readers of the Guardian’s online archive.

Apart from vigilance, the Guardian cannot do much more. Its editorial guidelines on conflicts of interest are soundly drafted, and freelances’ contracts bind them to comply. This case will doubtless serve as a bracing reminder for staff writers, freelances and editors.