Family lawyers have issued a warning to same-sex couples planning to rely on pre-nuptial agreements to protect their personal assets if they "marry" under the Civil Partnership Act next month.

From December 21 homosexual couples can have their relationships legally recognised under the Act, and the Government predicts that 22,000 civil partnerships will be registered by 2010.

As thousands of gay and lesbian couples plan to cement their relationships in the eyes of the law for the first time, a new trend is emerging, according to David Pickering, head of the family law team at Birmingham-based solicitors Cobbetts.

He said: "As almost one in two straight marriages ends in divorce, there is no reason to think that the picture will be rosier with gay and lesbian partnerships.

"Pre-nuptial agreements are becoming increasingly popular among heterosexual couples as people realise that nothing lasts forever. We get several inquiries every month and we can't see any difference to that sort of agreement being used between same- sex couples.

"There is a big gay community in Birmingham and we are expecting a lot of inquiries about pre-nuptial agreements as people think about registering their partnerships. "No one should assume a prenuptial agreement is watertight and guaranteed to give full protection, but it is worth considering and in some cases can be extremely relevant and useful."

The new civil status for same sex couples who register in the eyes of the law will ensure that each partner has similar rights to married couples including pensions, benefits, tax and inheritance.

Mr Pickering said: "Until the last couple of years, in this country pre-nuptial agreements drawn up for heterosexual couples did not have any legal standing in the event of a marriage breakdown and were not worth the paper they were written on.

"But times and attitudes have changed, and more recently, the courts have taken a more progressive attitude towards heterosexual prenuptial agreements, being inclined to give weight to them in court.

"This is a good start for the introduction of gay pre-nups, which in the light of the new legislation are likely to become common place."

But he said certain criteria must be met if couples wanted their pre-nups to be taken seriously at a later date.

"It is impossible to give a client a 100 per cent guarantee that a pre-nuptial agreement would be upheld in court, but it is possible to give the client a greater sense of comfort in this area by ensuring that each party receives separate legal representation and advice regarding the terms of the agreement and its implications," he said.

"Secondly, there must be no pressure or undue influence placed by one party on the other and thirdly, each side must be open and frank when disclosing their worth."

But even when all these conditions are met, there is no guarantee that a court will uphold the entire agreement at the time of entering into the agreement."

Mr Pickering said: "Other factors such as children being adopted into the relationship would significantly effect whether or not a pre-nuptial agreement would subsequently be upheld.

"It would be unacceptable for one of the partners in a relationship to rely on an agreement which was made when both parties had careers and there were no children on the scene, so a review clause should be built into the pre-nup."