Sincere condolences. However it would appear the transporting the ashes is unlikely to present much of a problem: the following is taken from the BA website:
Cremated remains can be carried on board our flights in either your hand baggage or checked baggage.
In order to comply with regulations, you will need to carry with you all necessary documentation, including a Certificate of Death issued by a competent authority from the country of departure. You will also need to ensure that the cremated remains are packed in a sealed outer box or case.
Please note: If you are carrying cremated remains in your hand baggage, full security procedures will be applied and the sealed box or case will be x-rayed at the airport security point.