There are two main options for hiring staff in the UK - full-time employee and freelance.
To hire someone as a full-time employee, you need to register with the tax office (www.hmrc.gov.uk) so that you can create a PAYE scheme for tax, national insurance, etc. You also have to think about various other regulations, such as minimum wage, working time directive, data protection, student loans, tax credits, Employer's Liability insurance, holiday pay, etc, etc. An accountant can do all this for you, for a fee, or you can do it yourself. The government websites and contact centres are generally very good. I always take care of this stuff myself, so I know what is happening, but YMMV.
The other alternative is to hire someone on a freelance basis, where they have a Limited company and it is a B2B relationship, so you don't have to worry about any of the employment responsibilities.