The EU's chief Brexit negotiator, Michel Barnier, is urging the UK to adjust its demands in the next few months, accusing prime minister Boris Johnson's government of making unrealistic demands.

"The truth is that in many areas [the UK] is demanding a lot more than Canada, Japan or many of our other [trading] partners," Barnier said during a forum in Brussels, referring to current international trade deals the UK is seeking to emulate.

"In many areas, it is looking to maintain the benefits of being a member state without the constraints," Barnier added.

"It is looking to pick and choose the most attractive elements of the [EU] single market without the obligations. We can not and will not allow this cherry picking."

Barnier's comments follow on from a UK official who said it was "obvious" the EU had to show more flexibility, after talks stalled.

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Under the terms of the UK's exit from the EU, both sides need to reach a deal by the end of October.

Top British officials are expected to meet Barnier on Friday, before Johnson meets European Commission President Ursula von der Leyen and the chairman of the 27 EU leaders, Charles Michel, later this month.

Barnier said Britain wanted quota- and tariff-free access to the EU, while diverging from rules that govern the bloc – a position that has always been a sticking point for Brussels.