With two million unmarried couples cohabiting together in Britain, it might seem the phrase "living in sin" could be ripped up and used as confetti. The law, however, has not kept pace with the change in social attitudes, and many cohabitees are at risk of financial heartache in the event of a break-up - regardless of the length of their relationship.
According to a survey by Skipton building society, 14 per cent of cohabitees mistakenly believe that because they live together, they have the same rights as married couples.
"People still think that after two or three years of cohabitation, they suddenly acquire the magic significance of a 'common law' husband or wife," says Miles Preston, partner at solicitor Miles Preston.
"But there is no obligation to maintain the other person - if no children are involved - and there is no entitlement to capital provision such as the part-purchase of a property."
Reform may be on the horizon: in September, the Law Commission completed the first stage of its review of the legal rights of cohabiting couples. But specialists warn that it could be years before there is any real change. Instead, they urge cohabitees to take their own steps to safeguard their interests.
"Sit down when you are still together to discuss how assets will be divided in the event of a break-up," says Jennifer Holloway at Skipton. "If you only address the issues when you have split up, the emotional trauma can make the process very difficult - things become personal and irrational."
If you have bought a home together, ensure your share of the property is recorded in a deed of trust. "This can be a simple statement - such as what proportion of the property you each own - which is added on to the transfer deeds," says Mr Preston.
He warns that if a home is bought in joint names and there is no declaration of trust, it is assumed the ownership is 50:50 - a view that is not easy to overturn.
If you want to go one stage further, you can draw up a "cohabitation agreement", which will cost between £300 and £400 plus VAT, depending on its complexity. "This is a contract between both parties that, as well as setting down your share of the property, will state what will happen in certain events [such as a split]," says Zoë Porter, head of the Live Together team at solicitors Foot Anstey.
A cohabitation agreement is not legally binding but should carry some weight if you do end up in court, as it shows evidence of intent. That said, the agreement is still taken to the civil, rather than the matrimonial, courts - which means less protection for the p0artner in the weaker position.
"Years spent looking after the home may not be recognised," explains Mr Preston.
When buying together, you can enter into two types of agreement: "tenants in common" or "joint tenants".
With the former, you own a specific proportion of the equity, so if you split up, the other partner will keep only their stake. Meanwhile, you can elect that your share passes to someone else in the event of your death.
If you are joint tenants, then you have an equal stake. If one of you dies, your share will automatically pass to the other owner.
Ms Porter says that over the past year she has seen a 20 per cent increase in cases where cohabiting couples have split up and are disputing who owns what.
She adds that while people are pursuing a more active approach to "netting their share" after a break-up, very few are taking measures to protect themselves while they are still together.
Kirsteen Margetson, 28, and Dave Tweedale, 30, have been together for five years and own their three-bed home in Wheathampstead, Hertfordshire, as joint tenants. "We have not drawn up a deed of trust or cohabitation agreement," says Kirsteen. "But our set-up works as we earn the same amount and have shared the cost of the deposit, furniture, mortgage repayments and bills pretty equally."
Kirsteen is sceptical about the agreements but says that if there was a big difference in income, or children were involved, it might be different. "It could make things easier if we ever did split up."