A couple who fought HM Revenue & Customs all the way to the House of Lords sparked a wide-ranging review of Britain’s tax system yesterday, after winning their landmark case.

Geoff and Diana Jones, who own and run Arctic Systems, convinced Britain’s highest court that structuring their IT consultancy to minimise their combined tax bill was legitimate.

Business groups and tax experts declared victory on behalf of the estimated 200,000 similar family businesses, but last night HM Treasury dampened celebrations with the promise of a wholesale reevaluation of the issue.

The Treasury said: “This case has brought to light the need for the Government to ensure that there is greater clarity in the law regarding the tax treatment of arrangements used by some taxpayers to achieve an unfair advantage. The Government will therefore bring forward proposals for changes to legislation.”

The Treasury will deliver a statement to Parliament on the issue today, although it was unclear last night which particular aspects of legislation it planned to address.

However, sources indicated that any new rules are unlikely to apply retrospectively, meaning that Mr and Mrs Jones’s victory in their four-year fight against the Revenue’s demands for back taxes remained intact.

Outside court, Mr Jones predicted that subsequent changes to tax laws would not undo yesterday’s success. He said: “Everyone has to pay tax. If the law changes and it starts from a particular date in the future, that is preferable to the arbitrary, backdated decision the Revenue made in our case. How they thought they could do this is beyond me.”

Although the Revenue was seeking only about £10,000 – revised down from an initial £42,000 demand – the case has direct ramifications for tens of thousands of other businesses structured in the same way. They will now avoid demands for back taxes.

Splitting ownership of a family business between a husband and wife and then paying the wife a low salary so she becomes a basic rate taxpayer, as the Joneses did, is a long-established tax-reduction method that has been accepted practice for almost 20 years.

As the wife takes a lower salary, there is more money left in the business each year to distribute as profits to shareholders. Also, as a basic-rate taxpayer, Mrs Jones’s share of the profits, paid as a dividend, were subject to less tax, therefore minimising the couple’s overall tax bill.

Although any existing wealth accumulated by husband-and-wife businesses through this scheme appears secure, the future survival of this kind of tax planning was under threat.

Paula Tallon, a director at the tax advisers Chiltern, said that the Revenue were “sore losers who don’t like getting beaten and so change the rules when they do”.

Experts predicted that the Treasury would attempt to revoke the special tax status that married couples enjoy.

Central to the scheme is a provision in UK law that allowed Mr Jones to transfer a half-share of the business to his wife while ensuring that any subsequent income she earned from that share would be taxed according to her tax rate as if the asset had belonged to her all along.

This provision, which applies to civil partners but not other kinds of partnerships such as father-and-son businesses, is now likely to come under attack.

Chas Roy-Chowdhury, head of tax at the Association of Chartered Certified Accountants, said it was likely the Revenue would apply a test to married couples to ensure that their arrangements were legitimate. This would involve comparing their circumstances with nonfamily companies, he said.

Mike Warburton, a tax partner in Grant Thornton, said: “They will probably remove the exemption that applies to married couples. If they do, some of the wife’s dividend income will be taxed as the husband’s.”

As a basic-rate taxpayer, Mrs Jones was taxed at 20.5 per cent on dividends, compared with 32.5 per cent for higher-rate tax payers.

Mr Warburton and other experts predicted that fine-tuning where to draw the line on how each partner’s dividend should be taxed would be very complicated.