Thank you for your reply. Sorry, I wasn't very detailed with the procedure I use.
For cows milk mozz (which works fine) i used unhomogenised milk from the supermarket - I use 1 gallon of milk, mix in with 1.5tsp citric acid, bring to 88-90F max, add the equivalent of 1/2 rennet tablet (in the form of rennet powder), stir for 1 minute and leave for 10 mins, then slice up, heat slightly and stir, then seperate in a cheese cloth/sieve, hang up to drain for 1/2 hr before cutting up and adding to 185F salted water and stretching till smooth, and then dunk in cold brine.
For buffalo mozz (again from unhomogenised milk) I have tried everything from 1.5tsp to 3 (!) tsp citric acid , decreased the rennet slightly to 3/8ths of a tablets worth, but nothing seems to work. I am beginning to think that as you said, good buffalo mozz will be impossible without a thermophilic culture. Does anyone know where this can be obtained in UK?