"The Conservatives have made a series of uncosted tax promises - tax bribes, " said Mr Clegg, referring to Tory promises to recognise marriage in the tax system, limit the National Insurance rise, freeze council tax and raise the inheritance tax threshold.

BBC: Nick Clegg launches Scottish Lib Dem election campaign

"If Congress doesn't do anything for ten years, in the middle of 2011, people would be getting hit with inheritance taxes and Congress could pass retroactive legislation eliminating the estate tax to make the system more equitable, " Edwards says.

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