If the death was expected, as the deceased had been ill for some time, it would be normal to contact their Doctor, who would then visit to certify that death had occurred and determine the cause. This may not happen immediately as the Doctor may be in his / her surgery, or death may happen in the middle of the night, in which case you may decide to wait until morning before calling out the Doctor or alternatively call 999 and upon the police arriving at the home they will call upon a police doctor to allow legal paperwork to be signed and then be released into the funeral director's care.
Later that day or the next, the Doctor will issue the relatives a form called the Medical Certificate of Cause of Death (form 11). This contains a list of who can register the death, known as Informants, at the local Registry Office and what information the Registrar will require.
If the cause of death cannot be determined then the Doctor will refer the death to The Procurator Fiscal to decide whether a post mortem will be required.