Question Author
"What if everybody followed your example and brought packed lunches into the cafe and each took a table for just a 70p milk shake ? "
They'd sell a lot of 70p milk shakes is the answer to that one :-)
And they wouldn't actually lose any money because no-one would have been buying any food anyway.
I know I am in the wrong, I don't deny that. However, I am a regular customer who never eats their own (or indeed any) food in there, and they know me AND it was quiet at the time. Plus the lady was really quite rude, which didn't help
Anyway, I'll take the answer as a "no" :-)