The terms and conditions say:-
Fast Track Upgrade (the "Offer") is available to you if you're an existing consumer Pay Monthly or Business customer (who signed up in an O2 Shop, through O2 telesales or through o2.co.uk more than three months ago) or simplicity customer (who signed up in an O2 Shop or through o2.co.uk more than six months ago) on O2 who is still within the minimum term of their contract and, for consumer customers only, has monthly subscription charge (including any data Bolt Ons) of more than £40 per month (an "Eligible Customer").If you're a consumer simplicity customer and you've been on simplicity for less than 6 months, but with O2 for more than that, then you are an Eligible Customer.
So yes you would be eligible
Thanks for that, I did look over the T&Cs earlier and noticed this. It's just confusing since an O2 Customer Services representative told me a different story over the weekend, whereas another confirmed what's stated above today. Perhaps they've had clarification over the weekend.