More companies will leave Britain as Brexit negotiations drag on between the U.K. and the European Union (EU), the secretary-general of the Organization for Economic Co-operation and Development (OECD) said.

Angel Gurria said Monday that until a deal can be agreed, the British economy will face ongoing headwinds and, as a result, chief executives will take action.

"A number of companies are moving elsewhere or at least partially moving elsewhere," he said. "And this is going to continue in the next few months, perhaps the next couple of years until the actual exit takes place."

The U.K. is set to leave the EU in March 2019 and EU chief negotiator Michel Barnier has said he wants to complete the terms of the departure by fall 2018. But this timetable has come under pressure from the slow progress between the two parties.