There is no statutory sick pay for the self-employed. Statutory Sick Pay is an employee benefit, and a sole trader is not an employee. If you fall ill the main fallback is New Style Employment and Support Allowance (ESA), a contribution-based benefit that depends on your National Insurance record.
Sole trader / self-employed - No Statutory Sick Pay. SSP is for employees only
Main fallback - New Style ESA (contribution-based) if your National Insurance record qualifies
ESA assessment phase, under 25 - Up to GBP 75.65 a week for the first 13 weeks
ESA assessment phase, 25 or over - Up to GBP 95.55 a week for the first 13 weeks
Plus 7 more in the full guide

freedomisntfree.co.uk/guides/self-employed-sick-pay-uk