To visit EU countries in the Schengen area, he needs a Schengen visa. He has to apply himself and attend an appointment in person. The process and requirements will be easy if you are already a British citizen. Check the embassy/consulate website of your destination country to find out about the procedures. In the UK, many countries have now outsourced their visa processing and document collection to third party companies like VFS Global.
Visit:
https://www.vfsglobal.com/en/individuals/index.html
For other countries which are not covered by VFS, you many have to check their embassy/consulate websites for more information.
Advice is given based on my personal research and experience only. Do NOT contact me via private message for immigration advice