Originally Posted by
Far Siren
You can purchase your ticket now and change your return to 28 March after you fly the first leg since the ticket is valid for 1 year from the date of purchase. There would be no fare increase, but you'd still have to pay the change fee.
If you buy from BA (by phone) and tell them you want to travel at later dates than are permitted by the system, they will make a note in the PNR and the change fee will be waived.