The Liberal Democrats are to propose "the most radical tax change any party has put forward in this country for generations" in their manifesto, to be published later today.

Danny Alexander, one of those who wrote the manifesto, told Today presenter Evan Davis that the plan, representing a £17bn tax cut, would "put money back into the pockets of those people who are struggling".

And he rejected comments by the Institute of Fiscal Studies (IFS) that the party's claim that "the poor pay more in income tax than the rich" is, as the IFS puts it, "meaningless at best, misleading at worst". Mr Alexander said that the party's claim was based on figures from the Office of National Statistics and showed that the percentage of earning paid by the richest and poorest had actually widened in recent years.

Mr Alexander said the party would raise the personal tax allowance to £10,000, reform Capital Gains Tax, end tax relief on pensions at the higher rate, introduce a "mansion tax" on properties valued at more than £2m and introduce a new aviation tax.

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