You must tell HM Revenue and Customs (HMRC) if you’ve stopped trading as a sole trader. You’ll need to send final tax returns.
How to tell HMRC ?
The form is really easy to fill in. You will be asked some basic informations, most of all your UTR and NI.
You have the capacity to complete this form because you are a sole trader.
By completing this form they’ll cancel your Class 2 National Insurance contributions and other contributions you may have.
Bear in mind that if you are not currently earning money from your sole trader status you won't have to pay taxes, hence don't think that you have to cancel your status during each non-working period !