Microsoft is rewarding Lumia fans in UK, if they refer their friends to buy a new Lumia 950 and Lumia 950 XL and the purchase is made. You should yourself be a Lumia 950 or Lumia 950 XL owner however to refer any friend, as it requires “Lumia Offers” app available on Lumia 950 or Lumia 950 XL.

Here is how it works,

Step 1 – Buy a Lumia
Buy and activate a new Lumia 950 or 950 XL.
Step 2 – Register for the offer and refer your friends
Sign in to the Lumia Offers app on your new Lumia and register for the offer by entering your email address, and accepting the Offer Terms & Conditions. Then recommend Lumia to your friends via Lumia Offers app.
Step 3 – Be rewarded
When your friend buys a new Lumia 950 or 950 XL, registers for the offer, and identifies you as the referring customers by entering your qualifying referral email address, you’ll both receive a £50 promotional gift card to the Microsoft Store.
The offer is valid till 16th March and here are some of the FAQ answered. Check the source link for full FAQ.

What is Lumia Rewards all about?
The Lumia Rewards Offer is a limited time offer that encourages Lumia 950 and 950 XL owners to recommend their Lumia 950 or 950 XL to their friends, and when one of the friends buys a new Lumia 950 and 950 XL, both the recommender and friend get rewarded with a Microsoft Store promotional gift card worth £50.

Where is the promotion being held?
United Kingdom

What is the timespan of the promotion?
Lumia Rewards program starts on February 16, 2016 until March 16, 2016 or as long as rewards are available.

Who can participate to the Lumia Rewards program?
Only people 18+, who have purchased a new Lumia 950 or 950 XL from an authorized Lumia seller in the United Kingdom. Returned or refurbished phones, or Lumia phones purchased from an individual person are not eligible for the offer.

Thanks Stan for the tip. Cheers!!