PRIME Minister David Cameron was "appalled” by the ugly scenes at the end of the England Under-21 match against Serbia, Downing Street said.The PM’s official spokesman said the government was giving its full backing to a Football Association complaint over alleged racist comments by Serbian players, and sport minister Hugh Robertson had written to UEFA president Michel Platini urging an investigation.Britain expects "tough sanctions” if racism is proved, the spokesman said.Commenting on Mr Cameron’s response, the spokesman said: "He was appalled by the scenes that we have seen in Serbia."We are determined to stamp out racism internationally and at home and we are giving our full backing to the FA’s complaint on this issue."Clearly it is for UEFA to investigate this issue but we would expect tough sanctions. If we are going to stamp out racism from football then it is no good giving derisory fines, as have been handed out in the past."It is not good enough to say that people should shake hands and forget about it.”England Under-21 defender Danny Rose wants Serbia to be banned after he complained of racist abuse and being hit by missiles in Krusevac.The Tottenham man, currently on loan at Sunderland, said he had been subjected to monkey taunts long before the violent scenes which marred the end of the Euro 2013 play-off.Rose was sent off after the final whistle for kicking a ball in anger in response to provocation as scuffles broke out involving Serbian supporters, players and other officials.Rose told Sky Sports News: "I remember getting slapped twice and then I got ushered away.Agencies