UK Business Visa Guide & Assessment:

If you wish to set up your own business in the United Kingdom, then you can apply for a visa under the Tier 1 Entrepreneur category. The category is exclusive to persons who want to come to the UK to establish their own business. To apply for a Tier 1 Entrepreneur visa you cannot be from the EEA – European Economic Area and Switzerland.
There are two kinds of business funds with which you can apply for an Entrepreneur visa.
If you have an investment fund of £50,000, then you can apply for a maximum visa length of 3 years and 4 months. From this category you can apply to have your visa extended for up to 2 years. If, however, you are converting from another category, than you can apply for an extension of up to three years. The Visa fee for this category is £874 by post while £1,093 for online application. The same will be applied for each dependent. If you belong to Croatia, Turkey or Macedonia, then your visa fee will be £1,038 for an online application while £819 for an application by post.

While on a Tier 1 visa you can participate in more than 1 business, be self-employed, and bring the family. At the same time you cannot receive public funds or be employed by another.
The other Entrepreneur visa category is when you have business investment funds of more than £200,000. But to be eligible, you have to prove that; you own the money, any third party ensures its availability to you or the funds rest in a joint account shared with your husband or wife. If you have invested a similar amount 12 months previously on a different visa, then you can apply for this category as well. To have your visa extended, the application should be made before the current visa expires. You will need to meet the eligibility criteria for receiving the extension. You can also bring family and dependent children with you.