Came across this:

As part of British Airways’ commitment to child safeguarding the following changes will apply for travel from 1 May 2018

• The minimum age of a person permitted to travel alone on British Airways will increase from 12 to 14 years of age
• This will apply to all new bookings made from 01 May 2018

In addition, all customers aged under 16 and travelling alone must complete a parental/guardian consent form prior to travel. The form will be available on ba.com from early April 2018 so customers can download, print and complete prior to travel.

• All customers aged under 16 years old, travelling alone on or after 01 May 2018, no matter when the ticket was purchased, should be encouraged to carry this consent form
• For tickets purchased after 01 May 2018, the customer must carry the consent form
• The young flyer must bring this from with them to the airport and carry it at all times
• The young flyer will be required to attach a copy of their parent/guardian's current passport to the form.