Hello all,
I would be grateful for some advice on the following.
I published a conference paper during my PhD studies and now wish to submit a revised version of this paper to a journal, is this acceptable? Note that the revised version has an improved discussion of the results presented in the conference paper, but the remainder of the paper including the results/findings hasn’t changed. I’m aware of the fact that it isn’t possible to publish the identical paper in multiple journals as it is considered unethical, but does the same apply if you’ve improved the paper (albeit only slightly) and are going form a conference to a journal?

I think this is pretty normal, even desirable. I've come across a ton of interesting conference proceedings that the authors never bothered to publish as a paper and it's frustrating to anyone who wants a real peer reviewed citation to follow up on. In my field, journal articles are typically more substantial (though not necessarily by much), so you might need to add some more content. If you were in a hurry to get it out the door you could always submit it with minimal revisions but be prepared to do more work on it if the reviewer thinks it needs more robust work.

I am writing a journal article at the minute that I published the preliminary results in a conference paper. I was told that you should substantially rewrite it and add significant data. I am not sure if I supervisor was being melodramatic but she told me that the majority of text needs to be changed to avoid copyright issues, reformat the graphs (again copyright issues) and add a lot more data to justify the extra contribution. Also, I think it is recommended to mention the conference paper in your letter to the editor and you don't want them to be able so see too many similarities at a glance.

I think this is a very grey area, and everyone will have a different view. I have just submitted a paper-based of conferences paper. The conference paper only had a quarter of the results of the actual paper. So in my case, there are new results added as well as a new discussion. As Rewt said (and I don't think he Pi is being melodramatic) you have to change a lot of the work and effort, tables and graphs., it not just a case of editing the text, you need to add something new. Personally, If it only a revised version I wouldn't submit it0 you ideally need to be adding something new. I was always told during my PhD, to give a little information in conferences proceeding as possible to make sure the work is publishable afterwards. I would also tell the editor of the proceeding and offer a copy/link to them if possible and highlight the difference between both papers.

Thank you for your replies rewt & Nead. As you pointed out Nead, it does indeed seem to be a grey area of sorts as I've encountered a few examples of journal papers in my field that are almost identical in content to previously published conference papers, i.e., no additional results/analysis and just textual modifications. Hence my question above. My supervisor is convinced that the paper is good enough for a journal so I think I’m going to go ahead and submit it along with a link to the conference paper highlighting the differences and see what they come back with. If further analysis/results are required then I can always add them at the revisions stage. Cheers for your replies guys.