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Tensions escalate

The Long Parliament proved just as difficult for Charles as had the Short Parliament. It assembled on 3 November 1640 and quickly began proceedings to impeach the king's leading counsellors for high treason. Strafford was taken into custody on 10 November; Laud was impeached on 18 December; Finch, now Lord Keeper of the Great Seal, was impeached the next day, and consequently fled to The Hague with Charles's permission on 21 December. To prevent the king from dissolving it at will, Parliament passed the Triennial Act, which required Parliament to be summoned at least every three years, and permitted the Lord Keeper and 12 peers to summon Parliament if the king failed to do so. The Act was coupled with a subsidy bill, and to secure the latter, Charles grudgingly granted royal assent in February 1641.

Strafford had become the principal target of the Parliamentarians, particularly John Pym, and he went on trial for high treason on 22 March 1641. But the key allegation by Sir Henry Vane that Strafford had threatened to use the Irish army to subdue England was not corroborated, and on 10 April Pym's case collapsed. Pym and his allies immediately launched a bill of attainder, which simply declared Strafford guilty and pronounced the sentence of death.

Charles assured Strafford that "upon the word of a king you shall not suffer in life, honour or fortune", and the attainder could not succeed if Charles withheld assent. Furthermore, many members and most peers opposed the attainder, not wishing, in the words of one, to "commit murder with the sword of justice". But increased tensions and an attempted coup by royalist army officers in support of Strafford and in which Charles was involved began to sway the issue. The Commons passed the bill on 20 April by a large margin (204 in favour, 59 opposed, and 230 abstained), and the Lords acquiesced (by 26 votes to 19, with 79 absent) in May. On 3 May, Parliament's Protestation attacked the "wicked counsels" of Charles's "arbitrary and tyrannical government". While those who signed the petition undertook to defend the king's "person, honour and estate", they also swore to preserve "the true reformed religion", Parliament, and the "rights and liberties of the subjects". Fearing for his family's safety in the face of unrest, Charles reluctantly assented to Strafford's attainder on 9 May after consulting his judges and bishops. Strafford was beheaded three days later.

Also in early May, Charles assented to an unprecedented Act that forbade the dissolution of the English Parliament without its consent. In the following months, ship money, fines in distraint of knighthood and excise without parliamentary consent were declared unlawful, and the Courts of Star Chamber and High Commission were abolished. All remaining forms of taxation were legalised and regulated by the Tonnage and Poundage Act. The House of Commons also launched bills attacking bishops and episcopacy, but these failed in the Lords.

Charles had made important concessions in England, and temporarily improved his position in Scotland by signing a final settlement of the Bishops' Wars, then securing the Scots' favour on a visit from August to November 1641 during which he conceded to the official establishment of presbyterianism in Scotland. But after an attempted royalist coup in Scotland, known as the Incident, Charles's credibility was significantly undermined.