https://www.gov.uk/food-business-registration"A food business is anyone preparing, cooking, handling, storing, distributing, supplying or selling food"
If your customers collect the meat directly from the abattoir or butcher then you probably have a decent arguement that you do none of the above.
If you collect the meat then take it to the customer then you are certainly distributing food. If the meat is vac packed and you are taking it directly to the customer then environmental health may consider you low risk and not be all that bothered but I'm sure they will still want you to register.
It's not a license you need, simply a registration with the council (which didn't cost us anything).