According to Christian tradition, Maghtas marks the spot where John the Baptist baptized Jesus in the Jordan River.
The royal couple are to visit a series of religious and historical sites before heading to Egypt on Thursday.
The British Embassy said last month that the visit was aimed at shoring up a century of “strong bilateral relations.” It is putting an emphasis on combating climate change in the wake of the Glasgow conference, as well as interfaith tolerance.
Jordan was established as an emirate and British protectorate in 1921 before gaining full independence in 1946. The countries have close diplomatic and security relations.