In order to benefit from a full state pension, a number of qualifying years is required. For men born after 6 April 1945, and women born after 6 April 1950, 30 qualifying years are needed.
A qualifying year is when you pay National Insurance or have a credit in the capacity of being either a parent, with a dependent child under 12 years of age, or caring for at least 20 hours, each week, for a severely disabled person.
It is highly unlikely that you would have achieved any qualifying years. If you have now returned to the UK and are resident for taxation, then you will begin to accumulate qualifying years either through employment or through a voluntary payment to purchase a credit by means of direct debit each month.
Without knowing your National Insurance credit history, it is impossible to establish what and if any State Pension benefit you have each accumulated to date. In order to establish how many qualifying years you have already accumulated, I advise that you request a state pension forecast from the Department for Work & Pensions, which is available from its website, dwp.gov.uk.