Which electoral register have you checked? The online version (at 192.com, or wherever) is the edited roll, from which anyone has the right to be excluded. However, the paper version (which anyone may consult at their local council office) is the full roll, listing the name of everyone who has complied with their legal obligation to vote. (Since the majority of people now remove their names from the edited roll, the full roll has over twice as much information)
A postcode is only ever allocated to a single road (or, in the case of very long roads, to just a part of that road). So putting the postcode into Multimap (or similar) will show the street. The full (paper-based) electoral roll is listed in street order so, if the guy has registered to vote, you should quickly be able to find the house number. So perhaps a visit to your local council office might help?
Chris