Hi Daniel,
Very helpful answer thank you - I had a good look through and was able to spot the obviously spammy ones and will be submitting them to Google Search disavow. However, that probably only makes up 200-300 of the 19K+ inbound links.
I think I can identify the main cause for the huge amount of links are from the same two domains. Quite literally, from rows 200 - 18,000 these two websites show up in various different ways, e.g. Staging sites etc. These are actually sites we work closely with. think it's an overlooked issue on their part.
I'm guessing I can't fix that from my end. Is it worth notifying them that there seems to be an issue with their website?
Also on a linked note - one of the sites for example, has the URL as an image link on EVERY page, now I feel as though that is a poor design choice on their part, or they are not using nofollow. Am I right in thinking I need to inform their webmaster that their links are creating negative SEO?
In some cases I followed the link from the data export sheet to the linking page, but couldn't find a link to our site anywhere. What might be the cause of that?