What’s the difference between 'British by birth' and 'not British but can be registered as British'?
This usually relates to children, so we’ll start from them. British by birth means the child is British because of his/her family. It can be because of a parent being British, or because of a parent who has an ILR and a has a child born in the UK (who will be British by birth). In this case parents can just apply for a UK passport (here meant as a ‘passport book’), in the same way as British parents apply: sending documents to IPS (Identity and Passport Service), paying a passport fee and getting a passport. Most British-born parents here would not even think about anything else but simply applying for a UK passport (‘a passport’) for their child, without even thinking how lucky the child is :o)) 'Not British but can be registered as British' means a child is not a British citizen when he/she is born, so parents could not just apply for a passport. However, in certain circumstances they can register the child, ie submit application form and pay some fee to the UK Border