David Cameron attempted to ratchet up pressure on Peter Hain on Sunday, insisting that the work and pensions secretary “would have to go” unless he addressed unanswered questions about donations to his deputy leadership campaign.

But the strongest Tory attack yet made on the beleaguered cabinet minister was partly undermined as Mr Cameron was forced to defend his shadow chancellor, George Osborne, over allegations that he, too, had failed to make necessary ­declarations.