If you are a self employed woman running her own business, and are genuinely your own boss, you will not need to think about many of the maternity rights. However, you may need to employ maternity leave cover to keep the business running while you are absent, and you may have worries about money. You may be able to claim Maternity Allowance. Working Families cannot advise you on employing someone, or about running a business, but you will find more information for small businesses on the Business Link website.
If you work for other companies as a contractor, you are not entitled to maternity leave, meaning you have no right to return to your job after your absence. However you are still protected by sex discrimination law, and if you are not being offered work because you have taken time off to have a child, you may have a sex discrimination claim.