CARE has strongly criticised the high level of family taxation in the UK.
The Christian social policy charity is concerned that the income tax threshold for families in the UK is lower in real terms than in 1990, despite pledges from the Government to support families by raising the income tax threshold.
Research from the charity shows that in 1990-91, the threshold for a single person under 65 was £3,005. This contrasts with £8,105 today, an increase of 170%.
By contrast, in 1990-91 the tax threshold for families, both one-earner couples and lone parents, was £4,725. In 2012 it is £8,105, an increase of just over 71%.
Taking account of inflation, the threshold for a single person is 24 per cent higher than it would have been if the 1990-91 threshold had been set in line with RPI.
By contrast, the threshold for one-earner couples and lone parents is 21 per cent lower.
The charity said the tax system remains "insensitive to family responsibility" and leaves the UK "in the worst place to facilitate the creation of an 'aspiration nation'".
In a report to be released next week, CARE will warn that the UK Marginal Effective Tax Rate levels on one-earner couple families and lone parent families is "significantly out of line" with most of the developed world.
The Taxation of Families report looks at international comparisons in 2011 and shows that the UK's METR on a married couple with two children and one stay-at-home parent is higher in the UK at 73% than in any other developed country.
The rate means that a singler earner household will have 27p from every additional £1 earned to spend on the home.
CARE chief executive Nola Leach said: "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 today's research.
"It is unfortunate that the Coalition Government still has not introduced the necessary legislation."
She is calling upon the Government to introduce a transferable allowance to decrease the tax burden on one-earner families and the high METRs faced by the poorest households.
"Unfortunately, time is running out. Leaving the change any later than the March 2013 Budget would provide insufficient time for the new arrangement to get properly up and running before the General Election," she said.
"The Government must now prioritise implementing its marriage commitment in Budget resolutions immediately following the 2013 Budget."