If you start a business with a business partner you and your partner(s) personally share responsibility for your business. You also share the profits or losses and any bills for things you buy for your business. 

Each partner pays tax on their profit share. Therefore you need to register the partnership itself with HMRC and each partner individually. 

A partner does not need to be an actual person, it can also be a legal entity, such as a limited company. 

What is needed? 

• A name for the partnership 
• An address for the partnership 
• Basic personal information about each partner 
• National Insurance Number for each partner 
• Start date of your activity 
• Business activity description