United Kingdom Immigration Law is one of the most strict in the world. The United Kingdom (UK) covers England, Scotland, Wales, Northern Ireland. (The Republic of) Ireland is a different country and has it's own Immigration law
In order to be eligble for UK Citizenship you must have lived there for a minimum number of years (depending on circumstances)
Commonwealth Nationals(
List of Commonwealth Countries) who have a grandparent who was born in the UK may enter the UK for a period of five years on a UK ancestry visa. This ancestry visa will open up the entire job market to you and will not carry the restrictions of a UK work permit.
You will have to prove your relationship, and this may require spending a lot of time hunting for old marriage certificates, birth certificates, etc.
The main criteria are that you are able to support yourself without access to public funds and are willing and able to work. It is advantageous, but not necessary, to have a firm offer of employment in the UK.
After five years continuous stay in the UK on an Ancestry visa you may apply for permanent residency as long as you still meet the requirements for the Ancestry visa and you have spent five years in employment in the UK without a break.
Once permanent residence (properly known as indefinite leave to remain) has been granted there are no time limits on your stay in the UK.
You should note that to keep your permanent residence you should not spend longer than two years outside the UK. You should maintain ties to the UK and should consider the UK as your home. If you continue to only spend short periods of time in the UK over many years it is likely that there will come a time when you will lose your indefinite leave to remain in the UK. It is therefore beneficial in most cases to apply for UK citizenship. You can normally apply for naturalisation as an UK citizen one year after being granted indefinite leave to remain and as long as you meet the residence requirements.
You will need to meet the following requirements to apply for naturalisation:
You must be aged 18 or over and are not of unsound mind.
You must be of good character.
You should be able to communicate in the English language (or Welsh or Scottish Gaelic). There are exemptions to this requirement, for example if you are elderly or mentally handicapped.
You should intend to live in the UK or in Crown Service abroad (working directly for an UK Government organisation), or be employed by an international organisation of which the UK is a member, or be employed by a company or association established in the United Kingdom.
As of November 1, 2005, you also have to pass the UK government's new
Life in the UK test before you can apply for citizenship.