PHP needs to be able to copy a file to that folder.... Fasthosts might be able to do something to allow it to work, but there is nothing we can do from within the code. They may be able to do something with the webuser account to allow it to write files to folders with 700 permissions.
If they could give you sample php code of a way to upload a file on their system we could look at it and compare it to what we do, but the code we use just does a standard php file copy.