Factual error: Despite the several episodes containing serious offences like murder, you never see two barristers on any side. It is usual with serious offences for each party to have one Queen's Counsel and a junior, and although there are exceptions, we never ever see this very common practice in any episode.
Factual error: There are several instances of barristers, judges and court officials wearing the wrong court attire. Ushers are seen in wigs, which they don't wear, the judges have their winter garments on, despite it being summer and vice versa. Similarly, none of the barristers are ever presented as "QCs" and yet several are wearing the QC silks, but none have the waistcoat which goes with it.
Factual error: An error which arises from having the same characters in different episodes is that the frequently-featured barristers vary the cases they deal with to a laughable extent. One Queen's Counsel (A barrister appointed as counsel to the British crown) was seen defending a murderer in one episode and prosecuting a trivial offence in another. Someone of this seniority would not fluctuate workload like this.