Financial advisers have been warned to take a client's family relationships into account to avoid costly mistakes.
Speaking at the Chartered Institute for Securities & Investment's accredited financial planning conference in London, Jane Cowley, a partner at law firm Gateley, said it was increasingly common that families were complicated, maybe with unmarried parents or stepchildren which could have a financial impact.
She said advisers should not assume two people were married, even if they lived together, had children and had the same surname because there is no such thing as common law marriage in the UK, despite the fact many people believe there is.
Ms Cowley said: "We believe your role, as well as everything else you do as a financial planner, is to understand family dynamics and relationships. You need to have an awareness of family law and an awareness of financial and tax implications in the event of relationship breakdown."
Figures from the Office for National Statistics show the number of cohabiting couple families increased by 30 per cent between 2004 and 2014, making them the fastest growing type of family in the UK.
There were nearly three million opposite sex cohabiting couple families and 84,000 same sex cohabiting couple families in the UK in 2014.
Ms Cowley said the growth of couples living together without marrying should lead advisers to encourage their clients, if they fall into this category, to create "living together agreements".
This is a legal document which sets out who owns what and how these assets would be dealt with if the relationship breaks down.
Ms Cowley also warned about the growing number of parents and grandparents using their assets to buy their children or grandchildren a house, known as the "bank of mum and dad".
In 2016 family and friends are estimated to have lent £5bn to their loved ones to help them buy a home, with parents contributing towards 256,000 property purchases.
Ms Cowley said most of this money tended to be given as a gift rather than a loan, but she said this came with pitfalls if the child was in a relationship which ended up breaking down because it would give parents less control over the assets.
She said: "A loan can always be forgiven. If you have nothing in place and it is a gift you can't even raise the argument in court, but if it is a loan you can at least raise the argument."
Martin Dodd, a financial adviser with Midlands Investment Agency, said: "I would be somewhat surprised if advisers don't take into account someone's family set-up already. There are so many areas of financial planning that you can get wrong if you have not made the right trust nominations, or the right expressions of wishes nominations.
"Advisers who don't take that into account are asking for trouble further down the line."