Everyone is entitled to free representation at the police station. This can be either under arrest or attending for a voluntary interview.
Following the interview there is no legal aid available until such a time as you are (hopefully not) charged. Any legal services you wish to use (for example pre-charge representation) in order to assist the closure of your case will need to be paid for directly.
If you are in the unfortunate position that you then get charged the option of Legal Aid then returns. The majority of people are entitled to Legal Aid to one degree or another.
Legal aid doesn’t always mean free legal services. Legal aid can also be a reduced fee legal services. It is means tested. However most average earners are entitled to either free or reduced fee legal aid. It is important that you supply your solicitor with all the relevant information upon request promptly in order that your claim for Legal Aid can be assessed.