It is illegal in London for anyone to tattoo a minor under the age of 18; therefore, no reputable tattoo shop will give a minor a tattoo. Some individuals do choose to ignore this law and provide minors with tattoos. These people probably do not advertise this fact openly to avoid legal trouble.
The Tattooing of Minors Act of 1969 states clearly that the only way a minor under 18 can legally get a tattoo is for medical reasons, as is sometimes done when a doctor performs a procedure that is not done for mere cosmetic purposes. Persons who knowingly violate this law are subject to legal penalties including fines.
The most severe penalty a tattoo shop could receive for breaking this law is loss of its license. As such, most London tattoo shops will ask any young person for proper identification showing the date of birth. Since the person performing the work is liable if caught tattooing a minor, a tattoo artist must be careful about checking for authentic identification before doing the work.
Any minor who is unhappy with a tattoo they received while skirting the law cannot get it fixed by a reputable shop until the age of 18.