A company must keep its records for 6 years from the end of the last financial year they relate to. If you report the gain yourself through Self Assessment, keep your records for at least 5 years after the 31 January filing deadline for that tax year.
Keep business records after closing
Which records to keep and for how long after your business closes or is sold
Other ways to pass on your business
If you are planning succession rather than a sale, a family transfer is taxed differently: gift hold-over relief and Inheritance Tax Business Relief may apply.
Pass your business to family
Capital Gains Tax, gift hold-over relief, Business Relief and handing over the running of the business