It's a cake obviously.
As it has no bicsuit in it, only biscuit sized. It's sponge.

A cake the size of a lasagne is still a cake, not a lasagne.
( Donkey Gums @mattcomedy, Thu 28 May 2009, 12:27, archived)

McVitties have been arguing it is a biscuit for years.
There is no VAT on biscuits but there is on cakes.
( Anthropos Was making beer on, Thu 28 May 2009, 12:29, archived)