I have just had confirmation from Technical Support at Spark that they are blocking downloads from MediaFire.
I discovered this after a day of thinking it was a problem with my PC and trying to fix it. I realised the problem was not specific to my PC when I tried it on several other PCs and had the same problem. I then tried it at a friends house on Vodafone and the file downloaded fine.
I then tried using a proxy and was successful in downloading the file so this led me to believe that Spark were the cause. Spark Tech support were reluctant to admit it but eventually did stating that the MediaFire downloads are being blocked for security reasons, the file I am trying to download is content I created myself and is of no security risk at all and violates no copy write laws but that doesn't seem to matter to Spark as they have taken the blanket approach of blocking all downloads from Mediafire.
If you would like to test this here is a link to a txt file I have uploaded just with the word "test" written in it. If you are on Spark please let me know if you are able to download it successfully.
I will be changing ISP as soon as my contact expires.