Speaking at an event last night, the former deputy to Alastair Campbell at Number 10 and director of corporate communications at BSkyB said the prime minister did not define the Big Society tightly enough and lost control of the message.
Allan said: "A poor example of effective political communications was the Big Society when Cameron said, 'You can call it liberalism. You can call it empowerment. You can call it freedom. You can call it responsibility. I call it the Big Society.'
"He managed to define it in so many different ways it becomes meaningless. He says right from the top that you can call it all these different things and he hasn’t really defined a clear message. As a result what was a perfectly admirable concept gets blurred and people have different interpretations."
However, Allan praised Cameron’s speech at the Conservative Party conference last year when he chose to tackle criticisms of his privileged upbringing with a "clear message".
At the conference in October 2012 Cameron said: "I’m not here to defend privilege, I’m here to spread it."
Allan said: "[Cameron] effectively ended up leading the news with that line. In that sense it was an effective piece of marketing of his brand from one position to another."
Allan was speaking at an event called 'Marketing & Communications: How Unique Can You Be?', which is part of the Enterprise Connect series of sessions to encourage entrepreneurship at King’s College London.