The Bees lost first-choice strike force Lloyd Owusu and Ben Burgess this summer because of a lack of cash.

But Downes has moved to improve his options by signing the 19-year-old from Fratton Park.

Vine is a product of Portsmouth's youth system and made 13 appearances for the First Division club.

Downes also has trialist striker Leon Constantine in his sights, but has yet to make a decision on the Millwall forward.