A function of the justice system in the UK and in most of the rest of the developed world is to ensure that everybody has access to a legal defence, regardless of the amount of money they have available to pay a lawyer. This legal defence is provided by qualified lawyers hired by the state to ensure that everyone has access to advice and counsel in a police station or courtroom for criminal matters, and is provided for free by the government, should the need exist.
Legal aid is something which will be organised for you as soon as you need it, so if you’re being questioned by the police or if you’ve been arrested, you can ask to see a lawyer, and if you don’t have the money to hire one they will have to provide one for you.
Legal aid can also be provided to people in cases of Civil Law, although this isn’t necessarily guaranteed for all people and all situations.