If you are self-employed as a sole trader or as a partner in a business partnership, then you must keep suitable business records as well as separate personal records of your income.
For tax purposes, the business records must be held for at least 5 years after the 31 January submission deadline for the relevant tax year. For example, for the 2017-18 tax year, when online filing was due by 31 January 2019, you must keep your records until at least the end of January 2024. In certain situations, such as when a return is submitted late, the records must be held for longer.
If you are self-employed you should keep a record of:
You don't need to keep the vast majority of your records in their original form. If you prefer, you can keep a copy of most of them in an alternative format, as long as they can be recovered in a readable and uncorrupted format. For example, a scanned PDF document.
If records are no longer available for any reason you must try and recreate them letting HMRC know if the figures are estimated or provisional. There are penalties for failing to keep proper records or for keeping inaccurate records.