http://en.wikipedia.org/wiki/British_Citizen
British citizenship by birth in the United KingdomUnder the law in effect from 1 January 1983, a child born in the UK to a parent who is a British citizen or 'settled' in the UK is automatically a British citizen by birth.Only one parent needs to meet this requirement, either the father or the mother."Settled" status in this context usually means the parent is resident in the United Kingdom and has the right of abode, holds Indefinite Leave to Remain (ILR), or is the citizen of an EU/EEA country and has permanent residence. Irish citizens in the UK are also deemed settled for this purpose.