Welcome to the "People do it so that's okay then" school of English, Mr Thomas Chivers. His argument goes: some good writers have misused "literally" "so we're wrong to criticise Jamie Redknapp" for doing it.
David Morrison makes a good point in the comments:
Writer and comedian Paul Parry was scathing about the Deputy Prime Minister's slip. He told Today: "This is probably the worst thing Nick Clegg has ever done. He's just completely misusing the word."
He added: "It's not about pedantry, it's about communication. The key thing is the word 'literally' is a safe word.
"We've got a wonderful, floral language. You can say that you've got itchy feet, that you'd kill for a cup of coffee, that you'd bring the house down, that you've got a frog in your throat, but ultimately you need to be
able to show that words have a literal meaning as well.
"There is no other word that means 'literally' and if the word 'literally''s meaning is eroded by all this misuse then there is nothing to replace it and we'll get a lot more confusion."