Early in 1628 the Parliament met.  During its first session, the Commons prevailed on the King, after many delays and much equivocation, to give, in return for five subsidies, his full and solemn assent to that celebrated instrument, the second great charter of the liberties of England, known by the name of the Petition of Right.  By agreeing to this act, the King bound himself to raise no taxes without the consent of Parliament, to imprison no man except by legal process, to billet no more soldiers on the people, and to leave the cognisance of offences to the ordinary tribunals.

In the summer, this memorable Parliament was prorogued.  It met again in January 1629.  Buckingham was no more.  That weak, violent, and dissolute adventurer, who, with no talents or acquirements but those of a mere courtier, had, in a great crisis of foreign and domestic politics, ventured on the part of prime minister, had fallen, during the recess of Parliament, by the hand of an assassin.  Both before and after his death the war had been feebly and unsuccessfully conducted.  The King had continued, in direct violation of the Petition of Right, to raise tonnage and poundage without the consent of Parliament.  The troops had again been billeted on the people; and it was clear to the Commons that the five subsidies which they had given as the price of the national liberties had been given in vain.

They met accordingly in no complying humour.  They took into their most serious consideration the measures of the government concerning tonnage and poundage.  They summoned the officers of the custom-house to their bar.  They interrogated the barons of the exchequer.  They committed one of the sheriffs of London.  Sir John Eliot, a distinguished member of the Opposition, and an intimate friend of Hampden, proposed a resolution condemning the unconstitutional imposition.  The Speaker said that the King had commanded him to put no such question to the vote.  This decision produced the most violent burst of feeling ever seen within the walls of Parliament.  Hayman remonstrated vehemently against the disgraceful language which had been heard from the chair.  Eliot dashed the paper which contained his resolution on the floor of the House.  Valentine and Hollis held the Speaker down in his seat by main force, and read the motion amidst the loudest shouts.  The door was locked.  The key was laid on the table.  Black Rod knocked for admittance in vain.  After passing several strong resolutions, the House adjourned.  On the day appointed for its meeting it was dissolved by the King, and several of its most eminent members, among whom were Hollis and Sir John Eliot, were committed to prison.

Though Hampden had as yet taken little part in the debates of the House, he had been a member of many very important committees, and had read and written much concerning the law of Parliament.  A manuscript volume of Parliamentary cases, which is still in existence, contains many extracts from his notes.