The European Patent Convention is an international (not European) treaty; therefore BREXIT will have no impact on the grant European patents (EPs) and the validation of EPs in the UK.
Patentees will still be able to obtain patent protection for the UK through the European Patent Office (EPO), which is not an EU institution, in exactly the same way as they do today. UK-based European Patent Attorneys will continue to be able to file, prosecute, validate and oppose EPs for clients before the EPO covering all designations as is the current practice.
UK national patents will not be affected.
There will be some changes to SPC law after Brexit and guidance on this can be found here. This guidance is relevant if you: