The Deputy Prime Minister Nick Clegg has previously ridiculed the idea of a tax break for married couples as "patronising drivel that belong in the Edwardian age".
The coalition agreement spells out that Liberal Democrat MPs can abstain on a plan to recognise marriage in the tax system.
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Bangladeshi immigrant Akayed Ullah, 27, is accused of strapping a crude pipe bomb to his body and detonating it during rush hour.
US tax reforms could breach international rules and damage world trade, Donald Trump has been warned by Chancellor Philip Hammond.
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