Substantial tax benefits accrue to those UK residents who are not UK domiciled. In fact, it is perfectly possible for a non UK national who has no UK capital or income to live indefinitely within the UK whilst legally avoiding paying any UK tax whatsoever. In practice this allows a non UK domiciled person to reside in the UK virtually free of UK taxes long as they have foreign sources of income. Foreign income can be converted into capital and periodical lump sums can be remitted to the UK free of tax. UK situated property can be converted into non UK property thereby escaping the IHT regime altogether by, for example, transferring UK property into an offshore company.
Domicile is a concept peculiar to English law.
A person is generally considered to be domiciled where he is deemed by law to have his permanent home. Under UK law a person must have a domicile and cannot have more than one domicile. A person will usually take his father's domicile at birth. This is his or her domicile of origin. UK persons moving abroad, then, have the possibility of establishing an alternative domicile of choice but to do so they will have to show that their new home abroad is permanent and that they've no intention of ever returning to the UK to live on a permanent basis.