When it comes to taxation on businesses, I am definitely a layperson. So the proposals I put forward here are just a starting point.
Sole traders. I have proposed elsewhere on this site that there should be two types of "sole trader/self-employment; private and public.
The public sole trader category will include councillors, members of parliament and members of the European Parliament whose income comes from public funds. They would be subject to the same tax rules governing private sole traders/self-employed people; allowable charges and expenses must necessarily be incurred in order to carry out their business, But they must also publish annual audited accounts in the same way that Public Limited Companies are required to by law. This should go some way to eliminating the possibility of an expenses furore involving MP's and councillors in the future.
I also propose that all types of businesses should have "Earned Income Relief" of say 2% of operating costs before a tax on business profits comes into effect. However, banks and other financial institutions would be subject different tax rules and regulation.
It seems that all businesses have a problem with cashflow which is exacerbated by late or non-payment by people and businesses for the goods and services that has been provided to them. It will be possible for a person or a sole trader or any business to take any other person or business to the small claims court. If the court finds for the complainant, THE COURT will pay the amount owing to the complainant; The person owing the money would be subject to pay what I call "Emergency Tax" on their personal salary or drawings until the owed amount plus court costs and penalty charges were paid. This includes the salaries of the Board of Directors of a PLC.