If you've not found the Openreach developer guides yet then it is worth a look on the website and a read through. Interestingly it says “We’ll supply all the Openreach materials you need to build and install the network on your site, for free.” Now this might only apply to developers but would be worth asking especially if Virgin were to offer their ducting for free.
There is also a note that says “For all Single Dwelling Units (SDU) duct must be terminated on the external surface of the property.” so I’d be aiming to build a chamber where the existing duct enters your garden (to save them digging up the pavement at my cost) and then a straight run with a swept end coming out the ground just outside the extension where you want the new cables to end up.

I’d start with a phone call to both saying you want to move the termination point and explaining that you’d like the ground works doing to fit with your timetable and see what they say. You might find the cost they come up with means it isn't worth you going to the effort of doing it yourself.
One more point, in your first post you mentioned ‘business’ and if these are business lines then I’d expect the cost to be more.

In reply to a post by fatmcgav:

That's good to know, thanks...

Did you terminate the ducts internally to your property? If so, how did you handle preventing water and gas ingress?

Thanks

So the product our builders used was Filoseal+

https://www.filoform.co.uk/filoseal-re-enterable-duc...

Came in an applicator kit...
https://i.postimg.cc/rFVYk3MS/IMG-9039.jpg

Thanks for the suggestion. I have come across the developer guide, but I missed the single dwelling note.

Will start making some calls soon to find out what options are.

And only the virgin connection is a business one, due to me working from home. But it was just connected into the preexisting brown box that was on the wall...

Cool, thanks for the link...

Will make a note for later 😊

I'm a big fan of doing a job right but do the connections actually have to move? A couple of decent lengths of Ethernet cable between the old location and the new is cheap and easy to install if the routers (or ONT if it is FTTP) can stay where they are now.
Would save a load of cost and effort but isn't as a nice a solution.

Yeh, I'm keen to try and make things as clean as possible.

I'm going to be digging up the driveway to run a new water and gas pipe anyways, so the digging isn't the issue...

I know they won't share conduit runs, but would they share a conduit box?
For example if I stuck something like this on my boundary and ran the conduit from it to the garage? https://www.drainagesuperstore.co.uk/product/naylor-...

In reply to a post by fatmcgav:

Yeh, I'm keen to try and make things as clean as possible.

I'm going to be digging up the driveway to run a new water and gas pipe anyways, so the digging isn't the issue...

I know they won't share conduit runs, but would they share a conduit box?
For example if I stuck something like this on my boundary and ran the conduit from it to the garage? https://www.drainagesuperstore.co.uk/product/naylor-...

Usually you want to maintain separation up to their network demarcation, but honestly I can’t imagine there should be any issue with that as it’s all within your own property boundary.