Yes. You may carry ashes with you on board the aircraft. These are permitted in your cabin bags and may be carried in addition to your normal cabin bag allowance, provided that a copy of the death certificate and cremation certificate accompanies them.
Please make sure that any ashes are very securely packaged inside a suitable container with a screw-top lid and that this is protected against breakage.
Ryanair will carry human remains, but only on the London Stansted-Knock route. If you would like to make a reservation, please contact Skytrader in Birmingham on +44 870 4422979.