Hi Jim,
I've just been looking at the https://www.o2.co.uk/extras/disney-plus page
It does say Yes, " Can I have Disney+ as an included or paid Extra if I’m already a subscriber?
Yes. As an existing Disney+ subscriber, you’ll still be able to choose a Disney+ Premium plan from O2 Extras (either three or six months on us if you join O2 or upgrade, for £7.99 a month (worth £10.99) and get a further £2 a month airtime discount during your contract term). Disney+ will get in touch shortly by email to let you know how to manage your subscriptions in order to avoid double billing."
I hope you have better luck than myself. To be honest last year I was subscribing directly to Disney + and had no end of problems when I tried to add Disney+ to my O2 to take advantage of the 6 months free offer and the £2 a month billing ddicount.
Neither O2 or Disney could help me. I went through various scenarios where Disney cancelled on their end and told me to re-register through O2, however every time I tried it came up with the message that the account already existed. O2 kept telling me to change my O2 username (email address) and that it would then go through. I tried 5 different email addresses and still couldn't take advantage of the offer.
I gave up in the end and re-registered directly via Disney with another email address and didn't get either the 6 months free or the addittional £2 a month discount. I've now downgraded my Disney+ subscription to the £4.99 Standard with Ads plan - I can't use that on my VM 360 box though as only the ad-free Premium tier, priced at £10.99 per month, is available for subscription through VM's set top boxes.