I would say most definetly a biscuit.
Ask anyone working for minimum wage at Tesco "where are the Jaffa cakes?" They will direct you to the biscuit aisle.
If they were cakes or you got a "special" store assistant then they would direct you to the bakery aisle where all the cakes generally occur.
Steer clear of store own brands there is only one true jaffa cake and that is made by Mcvities.
Sleep safe!