You must provide accurate, complete and truthful information when requesting a new Confirmation of Acceptance for Studies (CAS) statement.
This includes details of any previous periods of study in the UK. According to the 5-year cap imposed by the Home Office, degree-level students cannot obtain permission to study in the UK for longer than 5 years. PhD students pursuing their first PhD are exempt from the 5-year cap rule. However, if you were awarded a Postgraduate research qualification which is listed in part 4 of Annex 6 of the Tier 4 Migrant guidance, your studies are capped at 8 years.