Enclaves and exclaves - at a local level, what would be reasons for them to form?

I'm creating a setting, and it's got two United Kingdoms in it: our world's one (which remains at its current size) and a slightly larger United Kingdom, known as the Longlands, across the sea from it (its name is exactly what it means.

In canon, the United Kingdom is slightly larger, and made up of several islands; the main United Kingdom (our world's one), Northern Ireland, the Longlands and another island (still to be named).

The Longlands are basically another part of the United Kingdom, not any separate country, but they form part of England (and Scotland at the top).

Within the Longlands I was going to add some new English and Scottish counties, and at local level, local government districts (unitary authorities, non-metropolitan county, non-metropolitan district, as explained at The Other Wiki here, but also have some areas from mainland United Kingdom only accessible via the Longlands.

Currently, I've got a small part of Worcestershire only accessible via the Longlands, the in-story reason being that the land was owned by a wealthy family.

From a political geography standpoint, what would be a good reason for there to be enclaves and exclaves at a local level? (I'm not talking about at an international level where you have to cross through one country to get to part of the other, e.g. Point Roberts in the U.S. is only accessible via Canada, or Busingen am Hochrhein, a part of Germany only accessible via Switzerland.

This question is more about settings than characters.

edited 25th Feb '17 8:24:54 AM by Merseyuser1

First thing that occurs to me is a cultural or ethnic difference. The Donutole ward inside Donut-of-cake has historically been populated by a particular cultural group, for example, and the federal authorities basically decided "eh, they fill up our football league" and allowed it to remain autonomous.

Because one political unit has been expanding over time, and has ended up almost surrounding another one. Where I live, the City of Detroit has entirely surrounded the smaller cities of Hamtramk and Highland Park.

Have you made a map? I have a hard time picturing what you're describing.

Coming late to the party, but look at a map of Norwich City Council. Norwich administers the entire upper reaches of the River Yare, so cuts through other council areas leaving bits of them as detatched parts on the other side of the river. Over time and mergers many of these have disappeared, but there is still one left where Broads Council to the north of Norwich have an exclave south of the river.

A similar situation to Detroit is north-eastern Cambridge, where the city has annexed parts of the surrounding county leaving exclaves behind. Reminds me of a classic Calvin & Hobbes cartoon: https://www.pinterest.fr/pin/106749453650968243/

Also, look at the explosion of bits around northern Gloucestershire and the amazement of fragments around Ashby-del-la-Zouch before 1974. Go to https://wikishire.co.uk/map/ and turn on 'detatched parts'.

Enclaves and exclaves can also be historical artifacts. If the countries/polities arose from private property - such as European countries which were assembled by medieval dynasties - the present-day borders might reflect past property rights. These were often quite fragmented and could lead to non-contiguous territories or at least to arbitrary borders. Part of the Switzerland-Italy border between Lake Como and Lake Lugano are examples.