It is important to understand that a Tier 2 visa or now called a Skilled Worker visa is not a Spouse visa. Both are 2 complete separate visas in their own right. The Home Office recognises that you may wish to take up a second job apart from just the one you have been sponsored and issued a visa on.

As a consequence, if your secondary job does not exceed more than 20 hours doing the same work as the business you already work for, you will be fine to start a business or company. It would also be good practice to inform your employer that by taking up a second job it would not affect your work duties with the company.

Original Source: https://www.quora.com/Can-I-start-a-business-company-on-a-Tier-2-visa-spouse-visa-in-London-England/answer/My-Legal-Services-1