I've successfully put the virgin media hub 3 into modem mode which shows first a green light, then purple.

I separately connected via ethernet to the tplink, logged in, created new password and went to change mode and set it to access point mode.

It saved this and rebooted.

I logged in again and enabled the WiFi on the default settings. 

I then turned off the tplink and connected it's blue wan socket to the ethernet port 1 on the virgin media hub 3.

I turned back on the TPlink and waited. 

The tp WiFi is on and connects, as do ethernet devices connected to the TP.

However, there is no internet showing on the TP or any connected devices. The tp gateway field is blank and connected devices don't show a gateway either. 

Is there anything else I can try before returning the tplink?

I have tried different ethernet ports on the hub 3.