The government has provided clarification on the matter of whether UK workers attending events in the EU will require work visas. As it stands, a person may enter the UK for a period of less than six months using a standard visitor visa. However, they may not do paid or unpaid work for a UK company or as a self-employed person. Attending business meetings or conferences does not fall under this caveat and is therefore permitted.
Similarly, government guidance for UK nationals suggests that if you are visiting a country in the EU for less than 90 days in a 180 day period then a visa will not be required. The exception to this is if you are self-employed and providing a service in another country.