Professional couple Tony and Cherie Blair are at odds with each other - over the law.

Mrs Blair, who uses her maiden name Cherie Booth in her work as a leading employment lawyer, has flown in the face of husband Tony's government.

In a written opinion for the TUC she said the European Parental Leave Directive, which offers 13 weeks of unpaid leave to parents of young children, was not being implemented properly by Tony's ministers.

It brings to mind the curious professional-personal relationship shared by former strategist for Bill Clinton, James Carville, and his wife, Mary Matalin.

In 1992 Carville was leading the campaign to get Clinton into the White House while courting Matalin, an aide to then president George Bush. The couple married soon after.

And then there was last year's unlikely romantic coupling of Jane Smith and Duncan Hamilton - she the 27-year-old daughter of the former Labour leader John Smith, he the 24-year-old advisor to SNP leader Alex Salmond.

So how do couples like these square their home and work lives?

Denise Knowles, a marriage guidance counsellor with Relate, says rule number one is to keep professional and personal lives well apart.

"If you have a couple that are working in areas that are potentially against each other, if they are not careful, those difficult situations can start to affect things in their relationship."

This requires careful control by both people in the relationship, says Ms Knowles.

"We have all brought work home. If we have had a rough day, that can alter your mood when you get home."

Her advice to the Blairs, who celebrate their 20th wedding anniversary in March, would be to have a bath and wash away the cares of the day.

"It is important if you come home and you are concerned about your work that you make it quite clear that your short temper is nothing to do with your personal life.

Kept confidential

"But because of the confidential nature of the work, it could be difficult to share those things.

"In that situation you have to make it clear to your partner that it is nothing to do with them."

Women in particular tended to feel aggrieved by a partner in a bad mood after work.

"If the husband comes home in a foul mood, women tend to think, 'How dare they?' They immediately think it is something personal."

So far the Blairs have done well separating work and family commitments. For instance, on holiday they granted photographers brief access, but then they said, 'enough is enough'.

They made it clear the day-to-day goings-on of the Blair brood were strictly off-record.

"There have to be clear lines between private and professional lives because if they become intermingled, you do neither very well," says Ms Knowles.

Perhaps the biggest test of the Blairs' ability to juggle home and office lives will come in May when their fourth baby is due.

The PM has already pencilled in his paternity leave, and a break from their hectic schedules will ensure husband and wife can fully enjoy the sensation of becoming parents.

Cherie meanwhile, has said there is no question about her priorities.

"The children and Tony will always come first," she has said.