The president of the European Parliament has warned the UK it can't pick and choose which parts of the Single Market it wants to keep when it comes to future Brexit negotiations.

Reaffirming the EU's stance in London – where he met the opposition Labour leader Jeremy Corbyn among others – Martin Schulz said the longer the UK delayed the exit process, "the more entrenched the respective positions risk becoming".

"The best possible deal – ladies and gentlemen – with the EU, is membership of the EU," Schulz said, to applause as he delivered a speech to the London School of Economics. "Any other arrangement necessarily entails trade-offs. Perhaps it is easier to convey what I'm trying to say in culinary terms. There will be no 'a la carte'. Secondly, on free movement, I see a clear majority in the European parliament for insisting that the fundamental freedoms are inseparable. And especially no freedom of movement for goods, capital and services without free movement of persons."

Many Britons who voted to leave the European Union in the referendum in June want to see restrictions on immigration from the EU.

Schulz, who said Britain shouldn't be treated as a "deserter" after meeting Theresa May on Thursday, also warned that the European Parliament could veto any future deal.

The prime minister said after their meeting that she still wanted Britain to have a "close relationship" with the EU. She also repeated that no official move to trigger the exit process via Article 50 of the Lisbon Treaty would be made this year.

Downing Street has refused to back up a claim by Foreign Minister Boris Johnson that Brexit negotiations could begin "by the early part of next year".