The British court system

I am from the US, and was wondering how the court system works in the UK regarding defense and CPS barristers. I hadn't noticed this before on other series (am working my way through Kavanagh now), but it seems that Jo Mills (Jenny Seagrove) has worked both sides of the fence on this series. I realize this is not real life, and that JJD's court is sometimes a free-for-all, but can one be a prosecutor (CPS) and a defense brief (on different cases, of course)? However, I love the series, as I do ALL your UK detective/courtroom shows. I am a consummate Anglophile, and I am now hopelessly addicted to PBS, BBC, Netflix, Amazon and You Tube catching up with every one I can find. Thanks for any info.