iPhone deals all get voted COLD so I expect a backlash and minus-hundreds, but here is the best deal I could find for any sim-free top-end smartphone (Apple, Android, Windows etc).
To obtain 27months interest-free credit on any smartphone simply apply for a Sainsburys Credit Card. If accepted you get the following benefits.
*Pay 0% interest on purchases for your first 27 months
*Earn 5000 bonus Nectar Points if you purchases total >£800 within first 3-months.
*Collect 2 Nectar points per £1 spent on Sainsbury's shopping and fuel
Of course, must can purchase the phone from Apple, Amazon or wherever using your new credit card.
*iPhone 7 32GB - Purchase Price £599 = 27x £22.19pm
*iPhone 7 128GB - Purchase Price £699 = 27x £25.89pm
*iPhone 7 PLUS 128GB - Purchase Price £819 = 27x £30.34pm plus 5000 free Nectar Points (worth ~£25).
*Samsung Galaxy S7 Edge 32GB - Purchase Price £599 = 27x £22.19pm
*Samsung Galaxy Note 7 64GB - Purchase Price £699 = 27x 25.89pm (awaiting UK availability).