Well if you read the page they go through a few possible scenarios. If UK does a so called hard exit very few companies are prepared and there will be a rough transition period. Quoting from the page "As it stands, and if nothing changes, the default position will be for the UK to leave the EU without a withdrawal agreement on 29 March 2019 at 11pm UK time. This would mean there would be no transition period, and EU laws would cease to apply to the UK immediately at that time."

This will obviously have some problematic impact short term