On 08 February 2018, Her Majesty the Queen and her Privy Councillors signed off on the The Unified Patent Court (Immunities and Privileges) Order. This means that the UK is now in a position to ratify the UPCA. However, UK constitutional practice first requires the UK IPO to provide to the Foreign and Commonwealth Office, which is the Government ministry responsible, evidence that all appropriate legislative steps have been taken. After checking this evidence, the FCO will prepare the formal ratification documentation which must be signed by the Minister (Boris Johnson MP) and submitted to Brussels.
All this could be achieved in a matter of weeks although, due to the pending constitutional challenge to the UP/UPC package at the BVerfG in Germany, ratification is unlikely to be prioritised by the UK. Some sources are predicting ratification around Easter, when the UK will also formally ratify the Privileges and Immunities Protocol. It thereby becomes possible that the UK would be ahead of Germany and France in taking achieving this necessary precursor to the entry into force of the UPC.