While it is possible to live in the UK for many years without ever becoming legally domiciled in the UK, you will become deemed domiciled in the UK for tax purposes if you have been resident for at least fifteen of the previous 20 tax years.
Once deemed domiciled, it is no longer possible for an individual to claim the remittance basis. They must instead pay tax on worldwide income and gains, and are liable to UK inheritance tax on their worldwide estate, not just on UK assets.
If you become deemed domiciled, it may be important to maintain your foreign domicile under general law. For example, the tax treatment of any offshore trust you established will be significantly different if you subsequently become UK domiciled as opposed to deemed UK domiciled.