Hello Justin,
Might I suggest the German spelling for your ancestor most likely would be M�hlhaupt, not Mehlhopt, which appears to have been anglicized.
It sounds as though an official as at sometime has written down Mehlhopt in error or perhaps your ancestor just adopted the name because it sounds similar in English. You must have the correct spelling if you are to conduct any research in German records.
As there are only about 20 surnames listed with the spelling M�hlhaupt in the German phone book, there is a strong possibility that someone may be related, you should write to them. Check for addresses at:
For Surname Distribution Maps for Germany go to:
http://christoph.stoepel.net/geogen/en/Default.aspx
As you will see the surname is not common, you need to know the name of the Town or Village where you ancestor was born. If the events you are looking for took place in a large city, it is helpful to know the name of the parish to establish where the records are archived today, or if the LDS have filmed them. This narrows down your research.
In Germany there are no consolidated indexes for Birth/Deaths /Marriages. Prior to unification, you would possibly be looking for church books, each parish was responsible for their own records.
The country we now know as Germany was prior to 1871, made up of a large number of States, Principalities and Dukedoms, each maintaining their own records.
Do you have some evidence that your ancestor was born in Hannover? if so are you looking for records in the state or the city?
Until you can give the listers more clues it is difficult to advise you.
There may be some records held in England, the Anglo German Soc. may be of some help. Have you checked with them at: http://www.agfhs.org.uk/
Did your ancestor become naturalized in England or New Zealand? Do you have his marriage certificate or birth certificates for his children? Do they give you any clues to his place of origin?
Have you checked the LDS films of the Hamburg *Indirect* Passenger *Departure* Lists for ships sailing for England? These films include passengers who stopped at another European or British port before sailing to their final destination. About 20 percent of the immigrants leaving Europe took indirect routes.
I hope this helps,
Elizabeth