It is a variety but you can substitute.
How To Brew had the following info on the variety:
Name:
Whitbread Goldings Variety (WGV)
Grown:
UK
Profile:
Flowery, fruity, a cross between Goldings and a Fuggle.
Usage:
Often combined with other varieties in Bitters
Example:
Whitbread Best Bitter
AA Range:
4 - 5%
Substitute:
Progress, Fuggles, EKG