The Long Parliament was the name given to the English Parliament that sat from 1640 to 1660, with several breaks in between. It was called the Long Parliament because it was one of the longest Parliaments in English history.

The Parliamentary system in England during this period was a bicameral system, consisting of the House of Commons and the House of Lords. Members of the House of Commons were elected by eligible voters, who were primarily male property owners. The House of Lords was made up of hereditary peers and senior members of the clergy.

The Long Parliament was initially elected in 1640 in response to King Charles I's request for funding to suppress a rebellion in Scotland. However, the Parliament quickly became embroiled in disputes with the King over issues such as taxation, religion, and the power of the monarchy. This led to a series of confrontations between the King and Parliament, ultimately culminating in the English Civil War.

The Long Parliament was extended beyond its initial term due to the outbreak of the civil war, which lasted from 1642 to 1651. During this time, the Parliamentary leaders, including Oliver Cromwell, gradually gained the upper hand over the Royalist forces, and the King was eventually captured and executed in 1649.

Throughout the Long Parliament, there were several important Parliamentary leaders who played a key role in shaping the course of events. These included John Pym, who was one of the leading figures in the impeachment of King Charles's chief minister, Thomas Wentworth; Oliver Cromwell, who was a prominent Puritan and military leader; and William Lenthall, who served as Speaker of the House of Commons for much of the Parliament's duration.

The Long Parliament resulted in significant changes to the political landscape of England. The King was deposed and eventually executed, and England became a republic, known as the Commonwealth of England, with Oliver Cromwell serving as Lord Protector. However, the Commonwealth was not a stable regime, and after Cromwell's death in 1658, the monarchy was restored in 1660 with the coronation of King Charles II. The Long Parliament, which had sat for over 20 years, was dissolved, and a new Parliament was elected under the restored monarchy.

During the Long Parliament, which sat from 1640 to 1660, the majority of its meetings took place in London, although there were some periods where it met in other locations.

In 1642, the Long Parliament moved to Oxford, in order to be closer to the King's forces during the English Civil War. However, this move was controversial, as many members of Parliament felt that it was inappropriate to move the seat of government away from London. The move to Oxford also created practical difficulties, as many members were unable or unwilling to relocate, and communications with London were difficult.

There was never a situation during the Long Parliament where there were two separate parliaments representing the King and the opposition. While there were disputes between the King and Parliament, and there were periods where the King attempted to bypass or dissolve Parliament, the Long Parliament remained the only legally recognized Parliament during this period.

However, after the English Civil War, there were several periods where there were multiple competing parliaments. For example, in 1653, Oliver Cromwell dissolved the Rump Parliament (which had been elected after the expulsion of most of the Long Parliament), and replaced it with the Barebones Parliament, which was made up of his supporters. This Parliament was dissolved after only a few months, and was replaced by the First Protectorate Parliament, which sat from 1654 to 1655. Overall, while there were some periods where the Long Parliament sat outside of London, and there were disputes over the legitimacy of Parliament during the English Civil War and its aftermath, there was never a situation where there were two separate parliaments representing the King and the opposition.