Each island's political development has been largely independent from, though often parallel with, that of the UK,[7] and they are akin to "miniature states with wide powers of self-government".

The Isle of Man's Tynwald claims to be the world's oldest parliament in continuous existence, dating back to 979.

These two branches may sit separately or jointly to consider pieces of legislation, which, when passed into law, are known as "Acts of Tynwald".

[23] Unlike the other Crown Dependencies, the Isle of Man has a Common Purse Agreement with the United Kingdom.

As overseas territories were added to the land conquered by the British, a number of towns and villages began to request formal recognition to validate their importance, and would be accorded a status if deemed to be deserving such as a borough or as a more prestigious city by the monarch.

In 2021, submissions for city status were invited to mark the Platinum Jubilee of Elizabeth II, with Crown Dependencies and British Overseas Territories being allowed to take part for the first time.

[30] Certain types of domestic legislation in the Isle of Man and the Bailiwick of Guernsey, however, may be signed into law by the Lieutenant Governor, using delegated powers, without having to pass through the Privy Council.

In Jersey, provisional legislation of an administrative nature may be adopted by means of triennial regulations (renewable after three years), without requiring the assent of the Privy Council.

A unique constitutional position has arisen in the Channel Islands as successive monarchs have confirmed the liberties and privileges of the Bailiwicks, often referring to the so-called Constitutions of King John, a legendary document supposed to have been granted by King John in the aftermath of 1204.

[32][33] In 2005, it was decided in the Isle of Man to replace the Lieutenant Governor with a Crown Commissioner, but this decision was reversed before it was implemented.

This territory was added to the grant of land given in settlement by the King of France in 911 to the Viking raiders who had sailed up the Seine almost to the walls of Paris.

The Channel Islands remained in the possession of the King of England, who ruled them as Duke of Normandy until the Treaty of Paris in 1259.

John's son, Henry III, renounced the title of Duke of Normandy by that treaty, and none of his successors ever revived it.

The Channel Islands continued to be governed by the Kings of England as French fiefs, distinct from Normandy, until the Hundred Years' War, during which they were definitively separated from France.

Charles III reigns over the Channel Islands directly, and not by virtue of his role as monarch of the United Kingdom.

They are both categories of self-governing territories which fall under British sovereignty (the Head of State being the King of the United Kingdom) and for which the UK is responsible internationally.

The self-governing status of the BOTs evolved through Acts of Parliament and the creation of fairly homogeneous political structures.

[49] On 15 May 2023, the three coats of arms of the Crown Dependencies and the sixteen heraldic shields of the British Overseas Territories, were 'immortalised' in two new stained glass windows unveiled in the Speaker's House at the New Palace of Westminster.

The Speaker of the House of Commons, Sir Lindsay Hoyle, said: "The two windows represent part of our United Kingdom family".

By constitutional convention this is only done at the request of the insular authorities,[58] and has become a rare option (thus giving the insular authorities themselves the responsibility for good governance in the islands); the islands usually prefer nowadays to pass their own versions of laws giving effect to international treaties.

[43] Westminster[vague] retains the right to legislate for the islands against their will as a last resort, but this is also rarely exercised, and may, according to legal opinion from the Attorney-General of Jersey, have fallen into desuetude – although the Department for Constitutional Affairs did not accept this argument.

The Marine, &c., Broadcasting (Offences) Act 1967 was one recent piece of legislation extended to the Isle of Man against the wishes of Tynwald.

Baroness Hale further asserted this legal opinion in 2014 (quotation above), though she did not hear arguments from Crown Dependency governments in that case.

[63] The Chief Minister of the Isle of Man has said: "A closer connection with the Commonwealth itself would be a welcome further development of the Island's international relationships"[64] The Crown Dependencies have never been EU member states, including during the period when the UK was.

[65] The Common Agricultural Policy of the EU never applied to the Crown Dependencies, and their citizens never took part in elections to the European Parliament.

This was resolved after officials in the affected French regions were allowed to communicate directly to counterparts in Guernsey and Jersey.

[71] The UK requirement for EU citizens to present passports to enter the Common Travel Area resulted in a drop of day visitors to Jersey in particular.

Under Irish law, Manx people and Channel Islanders – who were not entitled to take advantage of the European Union's freedom of movement provisions – are exempt from immigration control and immune from deportation.

[74] The document was signed in London, England before a meeting of the British-Irish Intergovernmental Conference, putting the rights of both countries' citizens, that were already in place under an informal agreement, on a more secure footing.

The agreement, which is the culmination of over two years' work of both governments, means the rights of both countries' citizens are protected after Brexit whilst also ensuring that Ireland can continue to meet its obligations under European Union law.