Showing on my Platinum Cashback card only, looks like a targeted offer to certain accounts.
Spend £100+, get £20 back
Save to Card to get a £20 statement credit when you spend £100+ online and in-store at Harvey Nichols by 24/12/2016. Valid once per Card. Terms & payment restrictions apply.
Worth checking some of the other recent Amex offers if you haven't looked on your account for a while. Threads for those posted here - http://www.hotukdeals.com/tag/amex