In the end I have telephoned KE and was offered a refund (minus a £260 refund charge). I would usually complain about the refund charge because it is the airline, and not me, who has changed the conditions of the ticket and start an AMEX dispute. But it's now too stressful dealing with so many airlines and hotels for trips that have now been cancelled that I cannot add KE to the list of disputes.
What was their reason for 260 GBP refund charge? What class was the ticket? You are not allowed to enter the Philippines, so your ticket should be refunded free of any charge.