To be clear - as an example - Calor Gas

(sector)Row 1 column A (Empty) (Company) Row 1 column B "Calor gas" (from list 2)
(sector)Row 2 column A (Empty) (Company) Row 2 column B "Calor gas" (from list 2)
(sector)Row 3 Column A ("Business & Industrial") (Company) Row 3 column B "Calor gas" (from list 1)

I would like to create a formula that looks up Company(Column B) List 1 and corresponding sector(in column A)- then identifies matching company from list 2 (in the same column) and populates the empty cell in column A: with the correct sector from list 1 COLUMN A.