Cannot use port 21

[BigChiv]

I have moved from BT to Sky and can now no longer connect to a specific IP using port 21 unless I go via  a VPN and everything then works as expected. I have disabled the router firewalls and I have also disabled Broadband Shield but cannot make the connection until I go through a VPN. It seems to me that somehow the SKY router is dropping my connection.

Any Thoughts?