Imagine reading a controversial news story on climate change and later finding out that the scientist, whose findings you are reading about, had seen almost every word prior to publication. What if the story was about some too-good-to-be-true cancer cure? How about if you found out the researcher was running out of cash and had lodged a grant renewal request with their funding agency? Would it make you more sceptical about the story?

I suspect you might be, and with good reason. To serve readers best, journalists should be one step removed from their sources. Yet copy-checking is, to judge from a recent blogpost by pharmacologist David Kroll and a discussion on the mailing list of the Association of British Science Writers, relatively common practice.

It's a trap I've fallen into in the past. Either a scientist you have talked to insists on checking the final version of the story with the threat of "withdrawing" their contribution to your piece (it feels churlish to point out that they have already agreed to speak to you on the record) or, an hour or two before deadline you're struck by a creeping fear that somewhere, something is dreadfully wrong and so you call on one or more of your friendly sources to read it over.

And so, you might ask, what? Journalists should get the science right in their articles and if letting their sources look at the copy before publication is a good way to ensure accuracy, then why not?

Denying sources access to final copy before publication is one of the central principles of good journalism. Scientists who demand to see a draft or journalists who let them may be doing so with the best of intentions. But ultimately it betrays the reader.

Part of the problem is that many scientists interpret the journalist's request that they "check the facts and your quotes only please" rather loosely. Some are under the impression that because their lab carried out the work being reported, they have some sort of ownership of the subsequent coverage. This is not the case.

Reporters will give the story an angle that has their reader firmly in mind. The reader is not a scientist's first concern. As a result, researchers can often suggest changes that would flatten the tone, or introduce caveats and detail that would only matter to another specialist in their own field of research.

Even if a journalist is under no obligation to accept any suggested changes, there's a danger of getting locked into arguments with sources over whether or not a particular tweak is acceptable. Worse, a busy reporter with a looming deadline could simply end up making changes for the sake of pacifying their source.

The net result of such shenanigans is the same – the story suffers. That's not to say journalists should not get the facts right, but as science writer Ed Yong and Nature's Brendan Maher point out in the comment stream of David Kroll's post, there are other ways to do that.

But the long-term effects are worse: copy-checking imperils the sort of science journalism that everyone claims they want to see.

Imagine if a scientist were to claim that the pharmaceutical company that supplied him with the drugs needed for his research had no influence on the published work, despite being given full access to the manuscript before publication. "I made no changes to the paper that I didn't think were fair and reasonable and made the paper more accurate or complete."

Yeah. Right.

Yet by buying into the practice of checking copy with sources, science journalists are doing something rather similar: imagining that we are able to hold onto a degree of impartiality in the face of what is sometimes significant pressure for changes. It's the sort of thing that leads some in the profession to worry that science journalists (in the UK at least) have "forgotten how to be journalists".

Of course, most science hacks wouldn't dream of sending a remotely controversial story out to their sources. But scientists have a vested interest in the way their work is portrayed in the media. Practically any story has the potential to be "controversial", for example by having an impact on a scientist's reputation or their next grant application. A journalist, on the other hand, must try to be independent – and seen to be so – if they are to be credible.

By circulating copy freely to sources aren't we tacitly admitting that, unlike political or business journalism, say, science journalism is not to be taken seriously?

Ananyo Bhattacharya is the chief online editor of Nature. All opinions expressed here are his own and do not represent the views of Nature magazine