State the decision and dates clearly
Name the role and employer, say that the letter is formal notice, and give the notice period and expected final working day. Ask the employer to correct the date if your calculation is wrong.
Check the written statement or contract before sending. Keep optional holiday, final pay and handover wording only where it fits your circumstances.
Use the right route for difficult circumstances
Acas warns that its ordinary template should not be used without further advice when someone believes they have no choice but to resign because of an employer's serious breach. Those circumstances can affect notice and legal options.
This page provides a starting letter, not employment-law advice.
Keep evidence of notice
Proofread names and dates, sign if appropriate, then keep the copy you sent and evidence that the employer received it. PDF provides a stable final record.