This link warns you there is less help available than people claim. The article is a bit negative: you might get lucky.
Grants? They don’t exist.
Type ‘business startup [your town] into Google (for example ‘business startup London’). This may bring up some local help. Most start-up organisations are local and not national.
You can also try the Government’s search tool here: https://www.gov.uk/business-finance-support-finder
Charities and support organisations
Unlock: Helping people with convictions to move on in their lives by providing information, advice and advocacy.
St Giles Trust: provides help for ex-prisoners
Startup Now: Helps ex-prisoners with business plans and provides mentoring
Prisoners Education Trust Provides education in prisons
The Hardman Trust. Provides grants for prisoners, and might help you buy equipment.
Enterprise Exchange. Helps people from disadvantaged backgrounds become self employed or start a business to transform their lives. Especially prisoners and ex-prisoners. Based in Sussex.
Useful media and sites
The Record The online magazine for law abiding people with convictions.
Inside Time. The national newspaper for prisoners and detainees.