Gilbey’s is a lighter gin than Beefeater.
Starting with each gin’s alcohol content: Gilbey’s Gin is 37.5% ABV while Beefeater is 40-47% ABV depending on which market you drink it in.
As I mentioned in this post, Gilbey’s Gin has light, floral aromas of juniper along with hints of sweet orange while Beefeater Gin has big juniper character and strong citrus notes.
From personal experience, Gilbey’s Gin has a bit of a forgettable taste in the mouth while Beefeater is bound to make a stronger impression, be it positive or negative, depending on your personal preferences.