Besides all the good advices you will get here, including the legalese, a not-so-often mentioned thing will be “How good is your boss?” If your boss, the decision maker, so desires and agrees - this will be that you will work independently as a contractor and you earn better then being employed. I've seen that it is very common for contractors in UK to have their company (or Consultancy) and your company employ you thus saving on taxes. Your company gets into an agreemenet with your current employer/company and you work as the consultant/contractor.