The rule with forks seems fairly arbitrary - when you are using a knife you hold it in your right hand with the tines pointing down, as jimmyt described. Quite trcky.

But it's OK to put down the knife, when you've cut up the food, and to transfer the fork to the right hand. When in the right hand the fork is always tines up, making it much more convenient for picking up food.

I don't actually think this is directly class related, except insofar as worrying about such things is more a middle class thing. Posh people are quite likely to use their fingers.