Hello Andy Bates,
CIS is only a feature offered in our Small Business products, not Self Employed. If you need to use this feature, you will have to cancel you self employed account and take out an Online subscription. Please find attached our pricing guide for the product: https://quickbooks.intuit.com/uk/pricing/
You can also contact our Sales team through 0808 168 9533 if you would like to discuss the plans any further.