http://www.dixons.clara.co.uk/Certificates/deaths.htm
"The description of the informant has varied with time. In the early days, the informant was one of the following
1. someone present at the death
2. someone in attendance
3. the occupier of a house
4. the master or keeper of an institution
The person present at the death or in attendance (which meant they had been nursing the deceased or in close contact with them during their illness) was also usually a relative, but the early registrations do not give the relationship of the informant to the deceased.
It is always worth remembering with registrations before 1875 that an informant "present at the death", with a name you might not recognise, could be a married daughter that you have had no information on since she left home, or a granddaughter or grandson, son-in-law or any other relative likely to have a different surname from the deceased .
By 1875 the relationship of the informant to the deceased was given - together with additional qualifications such as "present at the death" or "in attendance". People not related to the deceased but present at the death still qualified, but only "present at the death" would be shown."
Interesting site