British Airways is now allowing anyone who has a flight booked which is due to depart up until the end of October 2020 to cancel it for free and claim a voucher for its value to be used on future bookings. (If you've booked since 3 March 2020, you can do this for flights due to depart up until 30 August 2021.)
You'll be able to use the voucher on flights which depart up until 30 April 2022. (For full info, see the BA website).
It's important to be aware that if BA cancels a flight, you're legally due a full refund. Yet if you voluntarily agree to a voucher for a non-cancelled flight,