If signing that little piece of paper marked "marriage certificate" is not an option, cohabiting couples buying a home together should sign other documents to secure their legal, tax and insurance interests in the property.

There is no such thing as a "common-law" husband or wife. Under both the legal and tax systems, cohabiting couples are treated as strangers and this may mean problems if, as homeowners, they fail to put the arrangements in writing.

Ms Darina White, of solicitors A&L Goodbody says: "When buying a house together cohabiting couples should consider whether they would purchase as joint tenants or tenants-in-common. There is an important distinction between them in law, particularly when one partner dies."

Joint tenancy is a 50-50 arrangement and upon one partner's death the property will automatically pass to the surviving joint owner as specified in the deed of ownership.

If partners are contributing unequally to the purchase of the home, or to future mortgage payments, a tenants-in-common arrangement allows this to be specified. On the death of a partner, co-habitees with this arrangement can dispose of their share amount as they wish under their will.

The Family Home Protection Act does not apply to cohabiting couples. Therefore, a non-owning partner is not protected if the owning partner decides to sell or mortgage the property without their knowledge, said Ms White.

Sometimes partners with sole ownership of the property decide to leave a "right of residency" for the survivor. This may cause complications since the eventual owner incurs a tax liability when the will writer dies. As the next of kin may object to paying tax on a property to which they have no immediate access, they may contest the will thus creating legal bills for both parties.

If there is no objection when the resident partner dies, the property will be disposed of according to the original will.

It is important for each partner to make a will, according to Ms Gemma Jacobsen, director of personal financial services division at KPMG. "If they don't make a will, there's no clear guidance and it goes to intestacy. Barring the existence of a spouse or children, the property would go to next of kin," says Ms Jacobsen.

"If one partner dies it goes first to the spouse, then children, under the law of intestacy and then to next of kin and the partner is not considered next of kin. If they bought it jointly, and are considered joint tenants it should go automatically to the other partner," says Ms Jacobsen.

Tenant arrangements between co-habitees do not affect the rights of either partner's children from previous relationships. "Children have an automatic call on their parent's estate irrespective of a will," she said.

In the event of the relationship breaking up, a joint tenant policy with mortgage protection is the best position says Ms Jacobsen. However, they will be taxed on their 50 per cent share of the property.

Tax Issues

There are several taxes that affect cohabiting couples differently from married couples - income tax, Capital Acquisitions Tax (CAT), Capital Gains Tax (CGT) and stamp duty.

When income tax is determined, both partners are assessed separately, therefore there is no transfer of unutilised allowances or rate bands as provided for married couples.

CAT may adversely affect cohabiting couples who own a property together unless they plan carefully.

"Problems may arise where a cohabiting couple purchases a property in joint names and one partner contributes more capital than the other, as after the exemption half the difference is a taxable gift," says Ms White.

These contributions may also mean a higher tax liability upon the death of one partner, according to Ms White. "If one partner dies and leaves his or her interest in the property to the survivor in the case of joint ownership, the surviving joint owner is taxable on the value of the interest he or she receives.

"This liability could be substantial and it is prudent to consider taking out a policy of insurance on the other co-habitee's life to cover all or part of this. In the alternative, the house may have to be sold in order to raise the money to pay the tax bill," she says.

The difficulty arises because the tax threshold for gifts and inheritances from non-married partners is just £12,860.

Mortgage repayments may also be subject to CAT. "Another problem area may arise where the cohabiting couple takes out a joint mortgage but only one partner is earning and makes the mortgage repayments. The portion of repayments made by the income-earning partner, on behalf of the other is likely to be a taxable gift," she said.

"None of the capital gains tax reliefs available to married couples are available to cohabiting couples," says Ms White. However, principal residence relief may apply to the co-habitees residence if it is owned and occupied by the person selling the property.

The transfer of property from one partner to another or into joint names attracts full stamp duty for cohabiting couples, she said.

Insurance Issues

Insurance should be a key aspect of the cohabiting homeowners arrangement, says Ms Kathy Dillon, director of LifeWise, an independent, fee-based insurance brokers. Generally, a married couple will take out a joint-life, second-death policy whereas co-habitees should look for a different policy arrangement.

"A couple who are buying a home together should take out mortgage protection cover on a joint life, first death basis. Therefore, if one partner dies the loan is repaid and their share of the property is passed to the surviving partner. Effectively, the lending institution is taken out of the picture and the property is owned by the surviving partner but there's a tax implication," says Ms Dillon.

A Section 60 life policy is a good way to approach this problem. "The policy is payable on death expressly for the purpose of discharging an inheritance tax liability," she said. An alternative to the Section 60 policy is right of residence discussed earlier. The tax implications make this a less favourable option.

Cohabiting couples planning to buy a home must think carefully about the legal, tax and insurance implications of such a decision. Each couple's situation is unique and seeking professional advice from an independent adviser is one of the best ways to ensure that your estate planning is handled properly.