PARIS (BLOOMBERG) - The Brexit negotiations aren't even over, but Michel Barnier is giving thought to writing a book on Britain's exit from the European Union.

"I think it would be worthwhile that I tell how I've lived these negotiations in more detail," the EU's chief Brexit negotiator told a business conference in Paris on Wednesday (Aug 26).

"I don't just want to tell how we've handled the consequences of Brexit, but also why we need to take time to look into the lessons of Brexit."

Barnier said that he has kept notes during the four years of negotiations and will probably begin writing next year.

In his speech, Barnier also hinted that negotiations over the EU and Britain's future relationship may stretch beyond a meeting of the bloc's leaders scheduled for mid-October as the two sides struggle to reach an agreement.

"If we want to ensure the ratification of this new treaty at the end of the year, we need an agreement around Oct 31," Barnier said.

"The clock is ticking."

The post-Brexit transition period expires on Dec 31.