Just a thought but might it be Upper Harrow in Middlesex. Not that there is a place called that but he might have known it as that. He is living in Middlesex at the time of the 1851 census & maybe the enumerator made a mistake...clutching at straws here.
Just had a look on the IGI & indeed there was a Joseph Wells baptised in Pepper Harrow;
JOS WELLS
Christening: 19 FEB 1797 Holy Trinity, Guildford, Surrey
JOSEPH WELLS
Christening: 07 JUL 1799 Peper Harow, Surrey.
Both extracted records,
jane