apt-get not getting proxy authentication

The first time I used Ubuntu, I had installed 8.04 (Hardy version)
and in this after I did export http_proxy=http://username:<email address hidden>:port (As I'm behind a firewall),
I was able to download anything using apt-get.

But, then, after I moved to Ubuntu 10.04 and now 10.10, I'm unable to use apt-get.
The only way I can install anything in 10.04v and in 10.10 is using Synaptic manager.
The command apt-get update tries to run and gives the error
Failed to fetch <repository url> 407 Proxy authentication required.

I have set the proxy correctly in System->Prefernecs->Network proxy and have pplied it system wide.
I have also entered the proxy settings in synaptic manager.
Mozilla browser opens and I'm able to browse the net too.

Only on command line, apt-get does not work even inspite of exporting the http_proxy variable.
I went through many solutions on the web and tried many things like adding the export http_proxy=....
in different files such as /etc/profiles.d/xxx.sh file in /etc/bash.bashrc and /home/binunun/.bashrc etc..
Nothing has worked so far on both 10.04 as well as 10.10