From what I have understood so far , you need a work visa so as to work there .But then the visa requires you to get a job offer first .The employer tena anasema hawezi kupa job offer kama hauko UK or not legally allowed to work there (work visa) .chicken and egg scenario .
With Brexit, UK companies are hiring directly from here in Kenya. They then are responsible for getting you a certificate of sponsorship which you will then use to apply for visa. In my industry they are desperately looking for people.