Sherlock, a three-patch problem

Sherlock, Series 01, Episode 01, A Study in Pink


Dr. John Watson: What are you doing? 
Sherlock Holmes: Nicotine patch. Helps me think. It's impossible to sustain a smoking habit in London these days. 
Dr. John Watson: That's good news for breathing. 
Sherlock Holmes: Ah, breathing. Breathing's boring. 
Dr. John Watson: Is that three patches? 
Sherlock Holmes: It's a three-patch problem. 


Like a five-pound note (a fiver) or a ten-pound note (a tenner)