Goodwill is an asset within the meaning of TCGA92/S21(1). This guidance explains the nature of goodwill and its treatment for CG purposes.
Halsbury's Laws of England, 4th edition, Vol. 35 at page 1206 states that:
The goodwill of a business is the whole advantage of the reputation and connection with customers together with the circumstances whether of habit or otherwise, which tend to make that connection permanent. It represents in connection with any business or business product the value of the attraction to the customers which the name and reputation possesses.