You must be a citizen of the United Kingdom since birth and must not hold (and must never have held) any nationality or citizenship (including joint nationality) other than British, British Overseas Territory or dual British Irish citizenship.
You must have resided in the UK for 7 years immediately prior to application.
Your parents/spouse must currently have UK citizenship.
Following the MOD announcement that the UK Armed Forces will now be able to recruit commonwealth citizens without the 5 year residency requirement, please note that the RAF continues to apply standard residency requirements for security clearance, ie, DV employment requires 7-years UK residency immediately prior to enlistment; SC requires 3-years.