Immigrationboards.com

Hi,

I've got a friend that is Lithuanian and got British Citizenship. However, he continues to use his Lithuanian passport everywhere and have never used or gotten a British Passport before.

Does anyone know at what point it will become a problem for her?

For context: Lithuania only allows one citizenship so if you acquire another one you 'lose' the lithuanian citizenship. But my friend basically won't tell them.

If he/she is British there are no restrictions - you are not subject to immigration rules, like EU citizens are, you basically don't have to prove status. Recommend friend applies for a passport. Let's face it if you obtain British citizenship, at considerable cost, one should make the most of it.
How friend handles the requirements of the origin country is a different story we can't really comment on.