1. The constitution is concrete and evolutionary, not abstract and revolutionary
With the brief and unsuccessful exception of Cromwell's Commonwealth, this country has never undergone a revolution in which the institutions of state were reconstituted on the basis of a new theory of government. When changes have been made, they have generally been incremental, and they have often been explained and justified as restorations of earlier practices.
The British constitution has therefore proved itself to be both flexible and stable. The other side of the coin is that it has been prone to develop anomalies and anachronisms which have sometimes taken a long time to correct. Growing debate about such issues has led to a series of unusually substantial changes in recent decades, including the adoption of the Human Rights Act, various schemes for reform of the House of Lords, and the devolution of power to Scotland, Wales and Northern Ireland.
2. Britain is a constitutional monarchy
To a large extent, the country is governed in the name of the monarch. The English monarchy can be traced back in some form to King Æthelstan, who became King of the English in 927 AD. Traditionally, Englishmen were defined as subjects of the monarch rather than citizens of the state, and this idea persists to some extent even today. Ministers and judges derive their authority directly from the Crown, and legislation takes effect only when it has received the Royal Assent. Legislation regularly bestows specific powers on the Crown, and the monarch retains a body of inherent personal powers (the "royal prerogative") - although in each case these are almost invariably exercised today on the advice of ministers.
So the monarch reigns; but he or she does not rule. As early as the 15th century, the eminent jurist Sir John Fortescue was expressly contrasting the English constitutional monarchy with the more absolutist monarchy of France. Several monarchs who went too far in the latter direction - Charles I being the best known example - lost both their thrones and their lives.
Restrictions on royal power go back a very long time. As everyone knows, Magna Carta (1215) limited the rights of the monarch, and Magna Carta itself looked back to the Charter of Liberties of Henry I (1100). The following words were attributed to the great mediaeval scholar Henry de Bracton (c.1210-1268) and were repeatedly quoted in later centuries:
The king himself ought not to be under man but under God, and under the Law, because the Law makes the king. Therefore let the king render back to the Law what the Law gives him, namely, dominion and power; for there is no king where will, and not Law, wields dominion.The monarch reigns, moreover, by the will of Parliament, as currently expressed in the Act of Settlement 1701. Already in Anglo-Saxon times kings appear to have been chosen by election. The notion that kings were appointed rather than born persisted at least to the reign of King John (1199-1216), and it was manifested again when Henry IV was offered the crown in 1399. A doctrine of pure hereditary legitimacy appeared with the assertion of the Yorkist claim in 1460 and the Jacobite claim after 1688, but both of those claims were defeated and abandoned.
3. The highest authority of the state is Parliament, which consists of the monarch, the House of Lords and the House of Commons
Parliament was already in existence by the 13th century, and its two chambers were sitting separately by 1341. Its origins may be traced deep back into history, to the Anglo-Saxon Witan and beyond. By Tudor times, the division of authority in Parliament between the monarch and the two houses had come to be embedded in the enactment formula of statutes:
The king our sovereign Lord Henry VII at his Parliament holden at Westminster... by the assent of the Lords spiritual and temporal and the commons in the said parliament assembled and by the authority of the same parliament hath done to be made certain statutes and ordinances in manner and form following.Much the same formula continues to be used today. Monarchs did also assert a kind of secondary power to make legislation by ordinance or proclamation, but this scope of this right was unclear and contentious, and little has been heard of it since the Glorious Revolution of 1688.
For a long time, Parliament was seen as providing a perfect combination of the three forms of government: monarchy, aristocracy and democracy. Today, the democratic character of the Commons is paramount. However, the dominance of the lower house is no recent development. Resolutions passed in the 1670s asserted the supremacy of the Commons over the Lords in financial matters, and these in turn drew on a tradition going back to mediaeval times.
Note that the doctrine of absolute, unfettered parliamentary sovereignty is a more controversial one - it can be traced back in some form to the 15th century, but it has equally been contested for several centuries. Nevertheless, whether or not Parliament is legally omnipotent, the notion that it is the highest organ of state is as well established as any doctrine of English law.
4. The legal system is based on the rule of law, and specifically on the common law
Roman law did not survive in England, save to a limited extent in the church and among academic lawyers. Instead, the country developed an indigenous system of "common law", founded not on the codes of Roman law but on the practices and precedents of the judges. The history of the common law is a very long one. Henry II (1154-1189) has a good claim to be the founder of the common law and the court system which administered it, and written legal precedents can be traced back to the plea-rolls of the 12th century.
The supremacy of the common law was qualified, to some extent and for some time, by the separate jurisdiction of the Privy Council and Court of Star Chamber. This independent royal jurisdiction did not necessarily perpetrate injustice, but it was discredited for ever by the excesses of the Stuart kings, and since the 17th century it has effectively ceased to exist.
Section 1 of the Constitutional Reform Act 2005 refers explicitly to "the... constitutional principle of the rule of law". The common-law legal system applies equally to everyone, although there have been and continue to be fierce battles to eradicate inequalities arising from sex, race and class. In principle, the courts are open to all, and no-one (except, in some circumstances, the monarch) is beyond their reach.
The common law has long recognised various individual rights and safeguards for them, including the rights to personal liberty and private property (which are mentioned in Magna Carta); habeas corpus (which has its origins in the Middle Ages and was codified in the Habeas Corpus Act 1679); and trial by jury (the first criminal jury trial was held in 1168, and the institution goes back to Anglo-Saxon times). In more recent years, these safeguards have been strengthened by the Human Rights Act and the European Convention on Human Rights, which was itself drafted under English influence.
5. The state has a relationship with the church, but an ambivalent one
England has an established church and many residual trappings of official Christianity, even though the secular character of modern English law has been officially recognised for at least the last century.
The relationship between church and state has always been problematic and open to negotiation, involving endless changes and conflicts, from mediaeval quarrels over civil and ecclesiastical jurisdiction, to the traumas of the Reformation, to the religious controversies of the Stuart period and the Commonwealth, to the advent of modern state-recognised religious pluralism.