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Following up on How do i get a British citizenship?, I realised that one of the requirements is
you’ll continue to live in the UK
When googling for the question I'm asking here, unofficial answers mention that once someone gets the citizenship, it's forever, irrespectively of where you (permanently) live. So, which of the two is true?
The requirement is one of intent.
Once granted citizenship, you are a UK citizen with all the rights that go with that - including the right to leave the UK, should you so choose.
If that is your intention from the start, then you would not meet the requirements to be granted citizenship.
By applying for citizenship, you are asserting that you do indeed intend to stay in the UK.
Currently, yes, a naturalised British Citizen can live anywhere in the world without losing UK citizenship - so long as they intended to live in the United Kingdom when they requested and were granted citizenship.
There's a strong precedent for this structure to remain intact, but the rules may of course change as the political situation changes.
The most useful reference documentation on this is the UKBA Precedent Based Scenarios document (see the PDF on that page, section 8: 'Deprivation' on page 25 (PDF Page 26)). Unfortunately the document is quite old, and doesn't take into account certain recent developments.
It's important that a person seeking naturalisation intend to remain in the UK. They should have "thrown in their lot" with the UK, and be intending to live in the UK for the rest of their life. In short, the oath of loyalty is more than a formality, and British Citizenship shouldn't be considered a tool to be acquired.
In certain circumstances, people have claimed and been provisionally granted citizenship, only to have it revoked because they have left the country before they took the oath. For more examples of this, see the "Precedent Based Scenarios" document referred to above. Specifically relevant sections are "NATURALISATION S. 6(1): FUTURE INTENTIONS" on page 46 (PDF page 47), and "OATH OF ALLEGIANCE" on page 70 (PDF page 71).
Once legitimately gained, though, citizenship is not currently stripped when people leave the UK for any length of time. This includes leaving the UK permanently.
The technical term for this type of loss of citizenship is "deprivation of citizenship".
Deprivation of citizenship is taken very seriously, and occurs very seldom. Between 2002 and 2013, 37 people were deprived of their British Citizenship. Generally, this occurs only in a fairly limited set of scenarios. One of the key considerations is whether retention of citizenship is for "the public good", and this is decided on a case-by-case basis.
For further details, see the "Deprivation" section of the UKBA Precedent Based Scenarios document linked above.
