You seem to have proved it's the Hub by getting the ONT LAN LED lit by connecting it to another port on the Hub. Unfortunately as above, only port 4 can be used. Connecting the PC directly to the ONT as previously suggested will prove this beyond doubt.
Edit
One last thing to try if you haven't already is to hard reset the Hub with a paper clip. It's not clear whether you did this or just reset it from the user interface.
https://www.bt.com/help/broadband/how-do-i-reset-my-bt-hub-to-its-factory-settings
Is it now working, as you have marked it as solved?
I’m a bit worried to do this as it’s a works PC, I work remotely from home.
As its still not working, I will unmark it as solved, as I assume you may have marked it in error. You only need to mark it as solved if you have a fully working service, as the moderators do monitor unsolved faults.
Difficult to suggest anything else, as it looks like a faulty smart hub 2. Without an alternative router to try, or the ability to setup a PPPoE connection, there is not much you can do.
There should not normally be an issue setting up a PPPoE connection, but its possible the work computer is locked down to prevent other connections.
One option would be to get a cheap router locally, there are plenty available, and see if that works, however if you intend to use the BT phone service, that will only work with the Smart Hub 2.
Sorry, hit solved by mistake. Still not working
If you're unwilling/unable to connect the PC directly then the only option is to replace the Hub. Get on to BT this morning & request that. If you're desperate to try to get online before that, have a look at Facebook Marketplace & see if you can pick one up cheaply locally. It's an expense you shouldn't have to make but you can resell it or keep it as a spare. Assuming that works, maybe push BT for an additional credit for failing to resolve it promptly.
If you really need to sort it out quicker, then this router should be available locally provided you live in or near to a town. https://www.tp-link.com/uk/home-networking/wifi-router/tl-wr940n/
Price around £27. It would require a very simple setup and if it works, it would prove that the home hub is faulty.
Currys seem to show it on their site.