Ireland has the second highest effective tax rate for one income married families in the developed world, according to new research.

The study, carried out by a UK pro-marriage charity, Care, showed that Ireland has a marginal effective tax rate of 64pc for such families.

This is based on a married couple, with two children, where one parent stays at home while the other earns 75 per cent of the average wage.

In Ireland, tax individualisation means a one-income married couple in general pays far more tax than a two-income married couple.

The report calculates the tax rate as the combined effect on a person’s earnings of income tax and national insurance increases and the withdrawal of State welfare benefits.

Only the UK, with a rate of 73pc, has a higher rate of tax on comparable single income married families.

The report, entitled ‘The Taxation of Families – International Comparisons 2011’, says that despite the Coalition Government’s pledge to help families by raising the income tax threshold – the threshold is when someone first begins to pay tax – families in Britain begin to pay tax at lower income levels in real terms, than in 1990.

Nola Leach, chief executive of Care, said Britain’s tax system does not support married couples.

She said: ‘Our tax system remains very individualistic and insensitive to family responsibility, compared to other Organisation for Economic Co-operation and Development countries.

‘Recognising marriage in the tax system, as promised by the Coalition Agreement, would help bring the UK back into line with its international counterparts and go some way to address the problems highlighted by the research.

‘It is unfortunate that the Coalition Government has not introduced the necessary legislation.’

The report authors say one-earner families and lone parents are also worse off in the current tax system than they were 20 years ago.