What does Brexit mean for patent applicants?

I agree with the first three responses posted. However, I would add that, after the UK leaves the EU (assuming that this will definitely go ahead), there might be some small changes with regard to patents in the UK. This is because it will then become theoretically possible for the UK to deviate from those (small) parts of patent law that derive from EU legislation - including provisions governing biotechnological inventions, as well as the "Bolar" exemption for studies and trials on pharmaceutical products.

This is not worth worrying about now, as there are many bridges to cross before we will find out what (if any) changes will be made to the UK's patent legislation on such points.

Of more concern for those working in the area of pharmaceuticals will be the effect upon "centralised" Marketing Authorisations (which, post-Brexit, will no longer be valid in the UK) and upon various forms of IP for pharmaceutical products (including Supplementary Protection Certificates and Orphan Marketing Exclusivity) that derive solely from EU legislation. The UK will need to generate new legislation in these areas, which legislation is likely to require rights holders (including patent applicants) to take action to secure (continued) protection in the UK. It will therefore be important for those affected to keep a close eye on developments in this area.

Further commentary can be found in my LinkedIn post on this topic (https://www.linkedin.com/pulse/dont-panic-mini-guide-brexit-vote-implications-ip-mike-snodin?trk=pulse_spock-articles).