In the event of no deal, the European Union will grant UK citizens visa-free travel to the EU and Schengen-associated countries for business meetings, training, attending conferences, sports/cultural events and short-term study for up to 90 days in any 180 day period.
If UK citizens are undertaking activity outside of these areas, or intend to stay for more than 90 days in any 180 day period, they will need to check with their EU host country authorities on their status. This is because visa and work permit requirements vary between Member States. This may involve some administrative processes and costs, and again this will depend on the country visited and the activity undertaken.
The Government has published guidance on travel, work and provision of services to EU and EFTA countries in the event of no deal, including guidance on business travel and visa requirements. This can be found on Gov.uk at the following addresses: