Is it ok to make mozzarella from pasteurised milk?
Yes, you can make mozzarella from pasteurized milk. You will want to avoid the so-called "ultra-pasteurized" milk if at all possible. 

The reason the ultra-pasteurized milk should be avoided for cheese-making is because the extreme heat denatures the proteins and they will not solidify into curd.  

This is US based, but is informative: 


  "The minimum legally required temperature for pasteurization [145°F], basically has no effect on the protein," explains Metzger. "But when you get to the 170, 175°F point, the casein and the whey proteins actually start to interact with each other." Those whey proteins, he elaborates, "are similar to the proteins in eggs—when they get too hot, they start to aggregate, and they take the casein proteins with them. What you're left with are proteins that won't coagulate into the kind of curds needed to stretch mozzarella cheese." (Source)