I had a request to make this into a new thread for the benefit of anyone else attempting to do the same, and as an alternative to using the Vodafone supplied Huawei HG659 router.
The AC66U router does do VLAN tagging on stock firmware, it's just not obvious unless you know where to go and what to look for. I believe other recent models will as well, such as the N66U, it's just a matter of looking for it as below.
Connect the patch cable from your ONT to the WAN port of the router, then log into it.
To start with, click on 'LAN' in the left column, then choose the 'IPTV' tab. From there choose 'Manual' from the 'Select ISP Profile' and then configure it as below.
Click 'Apply' and after it does its thing you will be connected, no further set up necessary.
FOR FIBRE & TV:
I have my Vodafone TV box connected to LAN 4 of the router, so to get it working you need to configure the box below the one above in the following way.
Click 'Apply' and once again once it's done its thing you'll have TV and fibre all set up working.
And on behalf of Vodafone: this setup is not supported by them and if anything goes wrong you're on your own!