Yes, I appreciate that. However:
Initially I went through the 3rd party site order process. When it got to the end of the order process it told me the order couldn't be completed and to call the options team.
I then tried doing it from BT's own site, rather than through the 3rd party site (similar offer, minus the gift card) . Same thing. Order cannot be completed, call the options team.
When you call the options team they say the offer is not available - it is only for new customers.
To clarify: the first sales person I spoke to knew all about the offer. He said "ah, that'll be the Black Friday Deal" and read out the offer to me. When he entered my details the offer was not there as an option to order.
He initially said that it was "probably" for new customers only. When I mentioned the Ofcom ruling he back-tracked a little and said that I SHOULD be able to have the deal, but when he entered my details into his system it gave him a series of packages available to me and the Black Friday deal was not one of them. He even got his Sales Support colleagues to try.
From this, I got the impression that if a sales person entered the details of a new customer the Black Friday deal came up as an option, but when the customers details showed them as an existing (out-of-contract) BT customer the Black Friday deal disappeared from the options.
When you tried it online it will have seen from your details you were an existing customer so wouldn't allow you to continue. I can't advise on what happened when calling though I'm afraid
Update: On 29th December, after chasing BT several times, I took a call from Laura at BT Enniskillen. She apologised for the long delay responding. After looking into the history, she could see that I SHOULD have been able to sign up for the deal I wanted (as some of the sales staff said) and that I was prevented from doing so by a "system glitch". She has refunded me the difference, so I'm back (almost) to the point I would have been had the issue not occurred in the first place.
Still think BT should give it's sales staff a bit of refresher training about who is (and is not) eligible for it's different tariffs as I got completely different responses from the staff I spoke to.