Hi ILNA,
Thanks so much for your helpful reply. It's understandable that they've disappeared from the rankings - as I understand, this redirecting to a non-relevant page would be classed as a soft 404 error and as there was such a large volume of traffic, and thus prompts to Google, it's no wonder it's affected rankings.
These redirects were not deliberately set up for these pages, as we had no need or want to redirect blog traffic to the homepage. It appears to have been something strange that has happened with our website, and we're still looking into that. What's also odd is that I've since spotted a link to our homepage in Google search results for one of the keywords a blog article - which was ranking in the same position as this new link - was targeted towards.
Anyway, I will take into account all your suggestions - we'll just need to look and see whether these articles start to rank again or some permanent damage has been done. Thanks again for your time!