Thanks Jason. I did initially get an error on the server:
413 - Request Entity too large
So I requested the host to increase the limit. They advised me that they'd increased the limit to 10MB (the sample files I have are around 3MB).
I've gone back to the hosts to double check they've changed any settings at their end. (I don't have access to the php.ini file)
Will have a look at the download stuff.