I killed a download by mistake and as it is such a big file, I don't want to start again. The file is still in my Incomplete folder, so is there any way to continue downloading it.

Thanks in advance for any help you can offer.

Very easy, just re-search the topic of the file. When the search results come up, the one you cancelled will have an icon that looks like a ripped/torn paper. Just re-downld it & your file will continue from where it left off. This is much safer than resuming from your library window which could have the side-effect of starting from 0%.