To activate this offer, sign up to Amazon Prime preferably with a new email (so you can take out a free trial) and add the XBOX One Console (only) to your basket.
Note: If you currently have a free trial for Amazon Prime on your GBP account, simply use the same login & password when you login into Amazon Germany (You may not get the same price quoted in the title, I recommend using Option 1)
There is no need for any codes as the price will automatically drop down to £269.76 (if paying in EUR currency)
However if you wish to just pay in GBP currency the price will change to £280.29
Either way this is still a decent deal
Link to the XBOX One Console Deal is in Comment #1