'Interracial and intercultural marriages are not intrinsically harder, but because the differences are more pronounced, there may be more surprises,' says Richard Gee, a counsellor at ReSource the Counselling Centre.

Every couple has to form rules for their relationship, he says, although for mixed-ethnicity couples, establishing that blueprint can prove more complex than for couples that share the same ethnic background.

'It is often trickier to negotiate aspects of the relationship because there can be so much more up for negotiation,' he explains. 'It requires more explanation and discussion between the two people as they may have completely different models of the world and the way society is organised.'

The issues are plentiful, including everything from money, religious beliefs, work and relationship attitudes to upbringing and the concept of family.

Such a long list of concerns may be enough to deter the faint of heart, but mixed couples say it can work in their favour because each individual is compelled to reflect on themselves and their values.

'You don't end up taking things for granted so much,' says Allan, who partly blames the complacency of his previous marriage for its failure. 'We were both from the UK and had lived together for four years before marrying. Everything was so straightforward that we just went along with it until it dawned on us some years later that things really weren't working out. A mixed-race relationship makes you rethink your preconceived ideas and talk to each other more to address what's really important before making decisions together.'

Although family hostility has been known to break up relationships, Gee says, in most cases he has encountered, the problems are more often down to the couple than to the influence of any external forces.

In 2005, more than 7 per cent of the 59 million married couples in the US were interracial, up from less than 2 per cent in 1970, according to research by Michael Rosenfeld, an associate professor of sociology at Stanford University.

'The rise of same-sex and interracial unions in the past few decades suggests changes in the basic structure of US society,' Rosenfeld wrote in the American Sociological Review.

'Young adults have been marrying later, and single young adults are much less likely to live with their parents. The independence of young adults has reduced parental control over their children's choice of mate.'

Although data on mixed marriages remains elusive in other parts of the world, Gee says mixed marriages will become even more commonplace in the future.

The chief problem that couples in interracial and intercultural relationships face is communication - not mere language, but the expression of self.

Different families have different rules about how they deal with issues. Some people have been brought up to talk about things openly, for instance, but others are more reserved and keep things to themselves, says Gee.

'This clash of styles can exist in all marriages, but it can give rise to further misunderstandings in mixed marriages because of the additional cultural differences.'

Linda Heaney Lau, a Scottish woman who divorced her Chinese husband, points out how even seemingly straightforward situations in daily life can be open to misinterpretation. 'I wasn't sure how much it was to do with the Chinese culture and how much it was to do with who my husband was,' Heaney Lau recalls. 'He was not a brilliant communicator. For example, I would have dinner prepared and be waiting for him, but perhaps being Chinese, he was not so vocal, and wouldn't call to say he wasn't returning.'

Despite that, Heaney Lau, who married following a whirlwind holiday romance in Hong Kong in the late 1970s, remains on good terms with her ex-husband and says she wouldn't trade the experience for the world.

Her daughter, Kirsteen Zimmern, currently working on a book of interviews with Eurasians, says she observed some of the most distinct differences in the way her parents showed affection. 'My mum would always be hugging and kissing me, whereas my dad was more reserved. That doesn't mean he doesn't care for me. He just shows it in a different way,' she says. 'The biggest problem in an interracial marriage is the way in which two cultures express love and emotion, and seeing as that is what makes a marriage, things can be quite difficult,' she adds.

'Every marriage has its challenges but an interracial and intercultural one where there are extreme differences does add more pressure,' says Zimmern, who spent her early childhood in a village in the New Territories with her extended family.

Ultimately, however, mixed couples say the biggest winners in a mixed union are the children, particularly when the parents are able to balance their two cultures.

'The whole issue of identity is so much more complex than just about my mixed blood,' says Zimmern. 'Eurasians feel immensely privileged. We are able to adapt to two different cultures easily and that makes you more of a global citizen. The ability to do that gives you an edge in both business and life.'

So appreciative is she of her bilingual culture that Zimmern, now a mother herself, is eager to pass on Chinese values such as respect for elders and the concept of face, alongside the Cantonese language, to her son.

'It's not only so he can communicate with his extended family, but also about him recognising his Chinese side. I want him to hold onto as much Chinese tradition as possible,' says the 29-year old mother.

Carol McNaughton Ho, a parent coach, married her Hong Kong-born Chinese husband when she was 21 years old. She has used her western values and understanding of Chinese culture to develop what she calls 'fusion parenting'.

'By fusing the best of eastern and western parenting, we can raise well-mannered and respectful young people who share their parents' cultural values yet feel able to voice their own ideas and opinions,' she says. 'Fusion parenting enables us to bring out the very best in our children and prepare our teens to face the ever shrinking world as responsible, independent young adults while retaining strong cultural values.'

Hong Kong, is, in many ways, an ideal place for such relationships to flourish.

'I've never had a negative experience being in a mixed relationship in Hong Kong,' says Heaney Lau. 'It's such a transient place and there is more openness - quite different from Scotland, where some of my Scottish friends were initially appalled by the fact that I had married a Chinese man and had a baby with him.'

Open communication is an essential ingredient in any relationship, but especially in an inter-ethnic marriage. 'The biggest piece of advice I could give would be to have the inner strength to give the other person the opportunity to be heard and accepted,' says Gee. 'Ask and listen to what your partner is saying without feeling threatened or attempting to change their minds.'

American Sarah Foster, who has just celebrated her 18th wedding anniversary with her Chinese husband, says that it can at times be easy to dismiss the power of difference.

'I was very naive when I decided to marry,' says the 42 year-old mother of two. 'I thought love would conquer all and didn't really think about how it might affect other people.

'To save yourself from arguments later, discuss the important issues beforehand as much as possible. It's easy to underestimate how different people can be.'