How Miliband memorised his 6,500-word speech

The Labour leader during a question and answer session yesterday (Susannah Ireland)

David Cameron memorably produces compelling oratory by delivering speeches on a full bladder, producing an inner tension and clarity that he believes keeps him focused – and his audience gripped.

He is said to have heard of the technique during a Michael Cockerell documentary about the late Conservative politician Enoch Powell.

Powell, best known for his infamous "Rivers of Blood" speech in 1968, performed his big speeches on a full bladder, explaining: "You should do nothing to decrease the tension before making a big speech. If anything, you should seek to increase it."

Ed Miliband achieved his own remarkable feat of memory this week by dividing his planned address into 11 sections and rehearsing each one individually in advance, it emerged yesterday. Mr Miliband started work on this year's speech – initially intended to run to 5,000 words and to last 50 minutes – while on holiday in Greece.

In the end, the Labour leader spoke for 15 minutes more than he planned and uttered an extra 1,500 words, increasing the workload of staff who transcribed the address.

As the Labour leader basked in plaudits for speaking for 65 minutes without notes, he insisted the technique demonstrated his authenticity. "In the end, if you really believe something you don't need [a text]," he said. The seeds of the speech, which his aides claimed could prove to be a political "game-changer", were sown exactly a year ago after his coolly-received address to the 2011 conference. He walked off stage in Liverpool and remarked to his team that he could have delivered the same comments – and to greater effect - without an autocue.

After deciding on the broad outline of his message to activists, he divided his planned comments into 11 sections of five minutes each, including "my story", "two nations" and "Olympic spirit". He consigned each to memory, but only ran through his planned speech in its entirety five or six times before his appearance in Manchester on Tuesday.

A colleague said yesterday that every time he practised the speech it came out slightly differently. "The idea was to make sure Ed had a connection with people, that he said what he felt rather than what he learnt," he said.

There were some downsides to the technique. To the dismay of green groups, he forgot to mention the environment – an omission he corrected in a question and answer session at the conference yesterday.

From Steve Connor, Science Editor: "It most likely Mr Miliband familiarised himself thoroughly with his subject matter, and practised what it was he wanted to say about it in terms of the meaning rather than verbatim."