Another Hub 5 Modem Mode Question... Sorry

Hi all, 

First off, apologies for the post but I can find no one single source of truth across these forums with lots of conflicting information. ...

The ask...

I have a hub 5, which has the ability to toggle modem and router mode. I can successfully turn the modem mode on, however when connecting a switch to port 1 [the only active port when in this mode], the router does not get sent a DHCP IP address, and as such can not connect to the internet via the hub 5 "modem". 

I can set a static IP on the WAN interface on the router, at which point it does see some traffic being sent both on TX and RX, however that is about as far as I can get. 

Speaking to Virgin technical support, which in this instance was not great (they were trying to sell me a gadget support contract and did not understand the networking questions I had), it was escalated to tech support management at which point I was told you need a business contract for modem mode to work. Not sure I totally buy that, however before spending another few hours at the terminal I thought I would check with the community. 

For info the switch is a tp-link omada.

I have tired in addition to the above :

1. cloning the hub 5 mac onto the router WAN port
2. setting a vlan tag on the network (i read somewhere it needed to be set)
3. communicating via ICMP  (no dns) to known public endpoints that would respond

Any help greatly appreciated.

Thanks!