The eventual consequences of Brexit depend on the deals the British government will make with the European Union. If your company works with long-term contracts, it would be wise to include special Brexit clauses. These clauses should cover, for instance, the validity of the contract once Brexit comes into force. You may want to change your contracts to deal with a changing trade situation; for instance, if the UK decides to adopt different product requirements.
The United Kingdom will become a non-EU country
As of 29 March 2019. The UK will no longer be part of the European Union. The EU will view the UK as a non-EU country. The expectation is that the EU and the UK will come to some sort of arrangement concerning trade. Use the period until 29 March 2019 to study the rules for trade with non-EU countries, and to prepare.
If you have dealings with the United Kingdom, you’ll do wisely to follow the developments. There are several platforms. The main governmental one is the Brexitloket (in Dutch):