Connecting to tekkit server chokes bandwidth?

[Ravenmorghane]

My Partner and I both play on our friend's Tekkit server, but lately he has been experiencing massive lag and a connectivity test has shown that while he is connected to the server, his download speed falls from 20 meg to about 2, making it lag so much its become unplayable for him. He has a better computer than I, we both share the same internet connection and it happens to him whether I'm playing or not.He is running on 64bit operating system and 64 bit java, as far as we're aware everything is compatible.

We can't seem to find anything online that might offer a solution so I was wondering if anyone has any ideas? He has checked the firewalls, tried reinstalling java, tried different versions of java, reinstalling tekkit launcher etc and we've run out of ideas.