One woman watching the TV conference coverage with interest last week knows better than most what life can be like married to a political leader. She is Elspeth Campbell, wife of former Liberal Democrat leader Ming. "It is terrifying and can be very difficult," she says. " On the one hand nobody minds being the centre of attention. But it can be very intrusive."

Elspeth, who has been Ming's constituency secretary for 20 years, praises Sarah's bravery and poise.

"I thought she was terrific. Sarah's a good friend of mine and I know for a fact she is not someone who courts publicity. She did what she did to help her husband and did very well. I am surprised that the public took to it for the Browns though."

With the attention now shifting to the Conservative party conference in Birmingham, the question is what kind of role David Cameron's wife Samantha will assume.

Early indications suggest that she will play up to the role of supportive wife, rather than as a player on the conference platform. Cameron has said that although he admires Sarah Brown for introducing her husband at Labour's conference, his wife Samantha will not be doing so in Birmingham.

He says she is great businesswoman, wife and mother, but not a public speaker.

Sarah Brown had been known to keep a low profile, but her background as a former public relations executive put her in a strong position to emerge from the shadows to aid her husband's ill-starred premiership.

Now with her performance and Gordon Brown's well received speech cutting his party's poll deficit by half, the stakes have been significantly raised. In the political game of one-upmanship there may now be a temptation for the Tories to propel Samantha into a more prominent role.

Elspeth Campbell warns:

"If the Camerons tried to do it they'd be laughed out of class. I think the public would see right through it. I don't think that Sam Cameron has stayed in the background anyway. There's not many photo opportunities that she doesn't get in."

At the Tory party conference in 2005, when Cameron delivered his famous speech without notes, Samantha was seen to have instilled the much-needed glamour that the party needed. Much was made of the tattoo of a dolphin on her ankle and her friendship with the hip-hop artist Tricky, who she met while at Bristol University. Sarah Brown has a more formal style, but has gained plaudits for her charity work.