BT HomeHub subnet issue

Hi,

I would like to use a different subnet internally than the subnet used by my BT broadband router.

I have a Cisco switch with 2 vlans, Vlan 10 and Vlan 20. Vlan 10 is internal vlan 20 is external. Vlan 20's ip address is 172.16.50.2 Vlan 10's address is 192.168.10.2.

The BT router has a leg in vlan 20 and it's IP is 172.16.50.3. Any PC in vlan 20 can access the internet fine. If a PC is in vlan 10 it can't access the internet.

I have route 0 on the switch which sends 0.0.0.0 0.0.0.0...

BT HomeHub subnet issue