Gordon Brown opened his speech by declaring that he wanted to talk about “who I am”.

There were some personal moments from the platform in Manchester, but not many came from the Prime Minister’s lips. Instead, it was his wife, Sarah, who uncharacteristically opened up and spoke from the heart.

In a masterstroke of public relations, as the lights were dimmed and the music turned low, Sarah Brown suddenly – to the surprise of all – took to the stage. Looking demure and dressed down in a middle-England-friendly grey T-shirt and black skirt, the Prime Minister’s wife received a standing ovation fit for a leader.

As the applause died down, she spoke softly: “I asked if I could have the chance today to talk briefly to you. One of the privileges of my life over recent years has been the opportunity to meet so many different and extraordinary people. These have all been great moments, often private ones, but always meaningful and I thank you all.”

As she spoke, hundreds of hearts around the room began to melt. It was the perfect opening, and Mrs Brown, the former PR guru, knew it. Will Samantha Cameron be under pressure to follow suit at the Tory conference?

Mrs Brown has given herself the task of humanising Gordon; over the years she’s worked tirelessly to bring her public relations skills to bear on her often stiff and starchy husband. On this occasion, she wasn’t going to take any risks.

Normally, it is the chairman of Labour’s national executive committee who introduces the Prime Minister. On Monday night, as the couple traipsed from hotel to hotel and function to function, the idea came to Sarah that she should be the one to welcome her husband on stage. What better way to soften up the audience before Gordon takes centre stage?

Aides said she slept on the idea, got up yesterday morning and tapped out some words, unaided and off the cuff. Roughly two hours before her husband was due to deliver the speech of his life, Mrs Brown told Mr Brown of her plan.

Her speech wasn’t just about warming the cockles of the delegates’ hearts. Far from it. For Sarah Brown is a shrewd operator and behind the “school mum” image, she had a much more serious message: “Stab this man in the back and you stab me.”

Why else would she remind people of when they were newlyweds? “I remember the warm welcome you gave me and Gordon at conference after our wedding.” And the coup de grace: “I’m so proud that every day I see him motivated to work for the best interests of people all around the country.”

There were echoes of Michelle Obama, who gave a speech before her husband, Barack Obama, at last month’s Democratic convention. But there was something a lot more brave and daring about Mrs Brown’s self-scripted appearance yesterday.

She concluded by reminding her audience: “Sometimes, in a world where there is so much to do, we don’t have enough time to celebrate what has been done.” Then, Mrs Brown simply but firmly introduced “My husband, your Prime Minister, the leader of the Labour Party, Gordon Brown.”

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