这次国宴是为了款待来访的英国首相。in honor of sb 向...表示敬意,为...的意思,这句话相当是说:The visiting British Prime Minister was the person in honor of whom the state dinner was given.
The visiting British Prime Minister was the person in whose honor the state dinner was given.
in one`s honor 向……表示敬意
the state dinner was given in honor of The visiting British Prime Minister
来访的英国首相是在其荣誉的人给予的国宴.