By law a death must be registered within 5 days, unless a Registration Officer says that this period may be extended or if the Coroner is involved.
Unless the Coroner is involved you will be issued with a Medical Certificate of Cause of Death by the doctor of the deceased, who will either be a General Practitioner or a hospital doctor.
You will then need to book on-line or contact any Cambridgeshire Registration Office to make an appointment, at which you will need to take the Medical Certificate, which will normally last about 30 minutes.