Does the BTw checker give you information about cabinet ports if so post the link here john.
just the http://www.dslchecker.bt.com
as your Vodafone you'll need to use the address checker but it gives the exact same info you need.
WBC FTTC Availability date will show "waiting list" if no free ports, and "available" when an order can be placed.
If it's a full cabinet and 1 free port becomes available then I wouldn't wait till morning to call an ISP, I would instantly place the order with your new ISP of choice. You can always call later in the day and amend any order/barter for a better deal.
I only know of BT Retail using the waiting list. Plusnet used to but now no longer place customers on the waiting list. This means my very full cabinet (waiting for 2nd cab to go live) still becomes "available" occasionally. It's usually showing full again by lunchtime, sometimes much quicker. This has allowed me to migrate twice, and notify a neighbour they can place an order.
Tip: You can get BT Infinity 1 Unlimited for £29.99/month for the full 12 months by going via topcashback. It says new customers only, but only the cashback part is rejected if you have already been a customer. The cheaper contract terms can't be changed. After calling later the same day they dropped this to £27.99. No good if you're not interested in BT, but handy for situations like yours where only 1 port becomes free. BT's system appears to book it instantly. I tried on 2 occasions with another ISP and the order was cancelled both times due to the cabinet being full, despite the checker becoming available. The ISP informed me their online ordering system does not reserve the port in real-time.
Hopefully your cabinet becomes available and you can migrate to another VDSL2 service. Shocking that Vodafone would rather throw you away as a customer rather than let you use your own modem.