Yvette Cooper MP, Labour's Shadow Home Secretary, said:
“Everyone across the country will be deeply disturbed and horrified at this shocking news. The idea that private investigators working for a newspaper would hack into the phone of a missing 13 year old girl is truly despicable.
“It is deeply distressing that the Dowler family, who have already been through so much, should now have to go through yet another media ordeal.
“I am now seeking immediate assurances that these actions did not affect the police inquiry into Milly Dowler's disappearance.
“These latest revelations make it imperative that the current police investigation explores every avenue to get to the truth with full co-operation from all involved.
“Once again, a phone hacking case raises very serious questions about media practices and police investigations, as well as politics and public debate.
“And as Ed Miliband said, last month, there is an overwhelming case, once the criminal investigation is complete, for a wider independent inquiry too.”