UK must be worse off after Brexit: Malta

Brexit negotiations must be transparent and honest but the UK must be left worse off when it leaves the European Union, the EU's presidency says.

The EU presidency says Britain must be left with a worse option than membership after Brexit. (AAP)

The European Union presidency says it is "imperative" that Britain be left with a worse option than membership once Brexit negotiations are over.

Prime Minister Joseph Muscat of Malta, which holds the EU presidency, said on Wednesday that negotiations must be transparent and honest.

"Negotiations should be fair for both sides but it is imperative that EU membership emerges as the superior option," he said.

"EU will not be 27 different opinions on Brexit but one common vision."

Muscat spoke as he met the EU's chief Brexit negotiator, Michel Barnier, in Valletta, Malta.

"Today is the first day in a very long and difficult road. The EU will look to establish a fair agreement for the long-term future of union members," Barnier said.