Boris Johnson has said he “won’t be deterred by anybody” from leaving the EU on 31 October.
The prime minister said he was “cautiously optimistic” of getting a Brexit deal, but the UK would leave by the deadline “whatever happens”.
Mr Johnson will meet European Commission President Jean-Claude Juncker and EU chief Brexit negotiator Michel Barnier on Monday for talks.
Parliament has passed a law forcing the PM to ask for an extension to Brexit.
Mr Johnson will have to write to the EU on 19 October to ask for an extra three months, unless he returns with a deal – then approved by MPs – or gets the Commons to back a no-deal Brexit.
But despite the new law, Mr Johnson said he would rather be “dead in a ditch” than ask for an extension.