The 'Instrument of Government' (the new written constitution of 1653) placed great power in the executive formed by the 'Protector' (the role of national governor set out in the Instrument) and the 'Council of State', many of whose members were military commanders. The country continued to be governed by military rule however according to the Instrument, the Protector was to summon Parliament at least once every three years. Also Parliament could not be dissolved without its own approval before a minimum of five months had elapsed.
When Cromwell's first Parliament met in September 1654, it was full of former Members of the Rump, "Commonwealthmen", angered by his dissolution of their government. They blocked proceedings over the next months as they discussed little else but plans to modify the Instrument to the advantage of Parliament. Cromwell dissolved this Parliament, which had passed no laws during its entire sitting, in January 1655.
King in all but name
In his second Parliament of September 1656, feeling against the Army-dominated Instrument of Government was running so high that in March 1657 some of Cromwell's civilian supporters presented to him the Humble Petition and Advice.
This was a constitution which reduced the power of the Council and recommended that Cromwell proclaim himself King. Cromwell declined the offer of the Crown, but the rest of the Humble Petition and Advice was accepted in May.
The 'other' house
Cromwell supported the creation of an other house in Parliament, which would consist of 40 to 70 people to be chosen by him and then approved by the Commons - a House of Lords in all but name.
When Parliament convened again in January 1658, Cromwell was faced with concerted opposition to the Humble Petition from a newly-forged alliance between the republican Commonwealthmen and segments of the Army. He dissolved this bad-tempered Parliament less than two weeks after it had first met, bitterly commenting as he dismissed it: "Let God be the judge between you and me".
Cromwell had proved himself no more successful than Charles I in handling Parliament, and he never summoned another one in the few short months before the Protectorate was thrown into turmoil by his death in September 1658.