Even then, the judge is still doing judging.
The jury determine if the defendant is guilty of charges or not, based on the evidence given during the trial. The judge still judges the admissibility of evidence, the conduct of the prosecution and defence, etc., and also determines the punishment or sentence, based on sentencing guidelines, if the jury find the defendant guilty of any charges.
https://www.cps.gov.uk/about-cps/how-a-criminal-case-works