The Meal Tub plot was a fictional conspiracy against the Duke of York, the future James II, dreamed up by Thomas Dangerfield in 1679 during the attempts to pass the Exclusion Bills. Dangerfield was initially believed in the atmosphere of panic caused by the Popish Plot. He was subsequently discredited.
Dangerfield claimed that he had been released from prison through the intervention of Lady Powis and Mrs Cellier, on condition that he assassinate the king, Lord Shaftesbury, and others. He pretended that he was to be engaged in manufacturing false plots to be foisted on those who were known to be unfavourable to the Catholic cause. One of these shams was to be based on a document hidden in a meal-tub in Mrs Cellier's house. The document was duly found where he said it would be. It charged with treason most of the leading Protestants, including the Duke of Monmouth, the Earl of Shaftesbury, and Sir Thomas Waller, the official charged with the search. In consequence of Dangerfield's accusation founded on this document, Lady Powis and Mrs Cellier were arrested, along with other prominent Catholics. Mrs Cellier's trial took place on 11 June, 1680. She was charged with high treason, but practically the only evidence against her was that of Dangerfield himself, and she had little difficulty in proving him an unreliable witness. She was found not guilty, and Dangerfield himself was arrested.