PortandLemon, you don't have to stay away - you just have to let them know that they are risking your custom. You could write something about the necessity for a company policy on this issue blah blah as it seems there are vast differences between one branch and another.
Here is the email I'm about to send, already a bit panicked about all the other shite I've got to do tonight but comments please in the next 15 mins, then I'm sending it and getting on with all the crap!
Feel free to copy the basics or word for word..
"I am writing to express my anger at the fact that the mother of a 3 day-old baby was told to stop breast-feeding in your Poole branch.
You are probably aware that breast-feeding is, according to the World Health Organization and the government, the best way for a baby to be fed. In this instance, the mother concerned was so embarrassed by her public humiliation that she has fel unable to continue breast-feeding her baby.
If some of your customers are uncomfortable with a baby being fed, then that is unfortunate. But were they to have expressed a similarly obnoxious complaint about another issue - made a racist comment, for example - you would, I am certain, have told them to keep their prejudices to themselves.
This is precisely the position that your staff should have taken in this instance, and I am astonished that they had not already received direction on Costa's company policy on breastfeeding.
Until today I have been a daily customer of yours, in E17 [google your nearest branch], but I will be having coffee elsewhere until Costa acknowledges its error and makes some reparation. I would suggest that long-term sponsorship of a charity which supports breast-feeding would be an appropriate response.
Yours sincerely
Onebat"