You will need to demonstrate that your business or business idea is innovative, viable and scalable, in other words, your proposal must demonstrate prosects of sustained success in the UK on a financial and commercial perspective. For new businesses, you will need to prepare a detailed business plan which reflects your business proposal.
You can also join a business after it has been registered with Companies House provided that the business has not already commenced trading. You would need to demonstrate you made a significant contribution to the business plan.
You will also need to obtain approval from an endorsing body and below you can find access to all of the current endorsing bodies:
https://www.gov.uk/government/publications/endorsing-bodies-innovator/innovator-endorsing-bodies
You will need to demonstrate access to at least £50,000 to invest in your business. Your endorsement body may provide you with funding of £50,000.