From shortly after his accession, King Charles I (r. 1625–49) found himself in a series of confrontations with his Parliaments, notably over the management of his war with Spain. In 1626, having failed to receive a grant of taxation for the war, Charles resorted to a forced loan, effectively a tax which had not been authorised by Parliament. This forced loan met substantial resistance, with some prominent gentlemen being imprisoned for their refusal to comply. When five of those men (the Five Knights) tried to secure their freedom by issuing a writ of habeas corpus, the Crown argued that it had the power to commit people to prison at its own discretion, without stating a specific, legal reason.
By 1628 Charles had no option but to turn again to Parliament. When it met, the House of Commons expressed its determination to secure a strong commitment from the King to observe the rule of law, since the Crown was held to have breached the spirit of clause 39 of Magna Carta. The Commons asserted their interpretation of the law by presenting Charles with a ‘Petition of Right’, rather than a formal bill, implying that they were claiming the subject’s existing rights, rather than creating new ones. The idea of the Petition of Right was suggested by Edward Coke, and it made explicit reference to the imprisonment of the Five Knights being contrary to ‘The Great Charter of the Liberties of England’. Once it had the reluctant assent of Charles – endorsed in his hand ‘soit droit fait comme est desiré’ – the Petition was regarded as having the same status as an Act of Parliament, and was therefore as strong a guarantee of the subject’s rights as Magna Carta itself.