Statutory notice is the legal minimum notice period set by section 86 of the Employment Rights Act 1996. From the employer to you, it scales with your service: one week between one month and two years, then one week per complete year up to a cap of twelve weeks. From you to the employer, the statutory minimum is one week (after one month of service), regardless of length of service.
Statutory notice is the floor. It's the minimum either side has to give the other when ending an employment relationship. Anything above it is contractual notice, which the contract can specify and almost always does. The longer of the statutory and contractual figures applies. For most office roles above the most junior level, the contractual figure is longer than the statutory floor, so the statutory minimum rarely matters in practice.
The statutory minimum from employer to employee scales with continuous service. Under one month: no statutory notice. One month to under two years: one week. Two to twelve years: one week per complete year (so three years means three weeks, eight years means eight weeks). Twelve years or more: twelve weeks, which is the cap. That cap means very long-serving employees aren't entitled to indefinitely growing statutory notice.
The statutory minimum from employee to employer is simpler. Under one month: nothing. One month or more: one week. There's no scaling with length of service. The reason for the asymmetry is that employee notice and employer notice serve different purposes. Employer notice gives the employee time to find new work; employee notice gives the employer time to backfill. The legal floor for each reflects what's considered fair without distorting contracts.
Statutory notice applies whether your contract has a written notice clause or not. If your contract is silent on notice, statutory applies. If your contract specifies less than statutory (rare and unenforceable to the extent below the floor), statutory still applies. If your contract specifies more than statutory, the contractual figure applies. The statutory floor is one-way: it can only raise the figure, never lower it.
There's a separate statutory notice question for redundancy specifically: the same s.86 figures apply. Statutory minimum redundancy notice is one week per year of service capped at twelve weeks. Many employers offer enhanced contractual notice on redundancy, particularly for senior roles, but the statutory minimum is the floor. The redundancy notice period calculator on this site handles this.
Statutory notice runs at the same time as PILON. If the employer pays PILON, the lump sum should cover the unworked statutory notice (plus the contractual notice if longer). Employers sometimes try to reduce PILON to less than the statutory minimum; that's unlawful. The statutory floor applies to PILON as much as to working notice.
Statutory notice doesn't reset on a role change within the same employer. Continuous service runs from your first day of employment with that employer (or with a predecessor if there's been a TUPE transfer or similar). So if you've been at the same company for ten years across multiple roles, your statutory notice from the employer is ten weeks (capped at twelve), not whatever applies from your most recent role start.
Practical recommendation: find your contract's notice clause and check whether the figure is above the statutory minimum for your current service length. In most professional roles it will be. If your contract is below statutory (very rare), the statutory figure overrides. If your contract is silent on notice, statutory is the only figure. The notice period calculator on this site uses whatever figure you select.
General information about UK employment law. For your specific situation, contact ACAS or an employment-law solicitor.