Any information about your source?

I don't think you can read too much into information supplied by customer services. They are probably trained to give standard, legally compliant replies. EN standard dictates a minimum cetane, but ultimate may still be above their standard diesel. One thing I am aware of is that cetane improvers of the kind BP chuck into their product, deteriorate rapidly with age and as very few customers buy ultimate nowadays, it stays in the forecourt tanks a long time and BP probably realise a lot of customers end up buying old diesel that has very little cetane boost from standard.