The UK ratified the Unified Patent Court Agreement (UPCA) on 26th April 2018 despite the Brexit vote and the currently ongoing negotiations for the UK to leave the UE.
Only the German ratification is now missing for the system to go alive, as France has already ratified the UPCA. However, Germany’s ratification has been further delayed since the constitutional complaint against the ratification of the UPCA (End of March 2017). If the German Federal Constitutional Court (FCC) decides not to admit the complaint, the German ratification procedure can resume (within approx. 6 months), still possibly before Brexit day (29th March 2019). If the FCC admits the complaint Decision, the decision will not be expected before end 2019 (may be even much later if the FCC refers the matter to the European Court of Justice), and the UK will have left the EU by that time.