The other answer? Smell it and look at it, and it also depends whether या not its been opened. I'd say no about drinking the milk- chuck it away, its not सुरक्षित for any person या pet to drink. One दिन आप could get away with, two no.
That depends on the दूध acutually. 'Sell द्वारा Date' is the governments doing, which states the law requires the खरीडिए to sell the products द्वारा this तारीख, दिनांक before they reduce and try and get rid. Two days after reducing and the product is still there and it must be thrown as waste. 'Best द्वारा Date' is the manufacturers law, that is put on each product as a GUIDLINE ONLY! Plenty of products, such as cheese, milk, meat, eggs etc can last for a full week AFTER the BBD before going bad. But that depends on storage, how आप handle the product (say if आप keep your eggs in the fridge and need to हटाइए them everytime to get something at the back etc).
But with anything आप buy, fresh/frozen etc must be carefully tested and tried before and after the best द्वारा date. I'd say give it a sniff see if it smells like cream या stronger then normal and if so take a teaspoon, pour a small amount onto the teaspoon and just touch your tongue to the liquid. If it tastes a little funny then i'd say that's a definate no and to chuck it. But if it tastes okay then i'd say go for it. But like i said, best द्वारा तारीख, दिनांक and sell द्वारा dates are laws from the government and guidlines only. In England, the government is actually planning on getting rid of the best द्वारा dates as that is a huge factor in खाना going to waste that could have been eaten.