Theresa May is due at a summit in Brussels, hours after Conservative rebels in the Commons defeated the government in a key Brexit vote.
MPs backed an amendment giving them a legal guarantee of a vote on the final Brexit deal struck with Brussels.
One rebel, Stephen Hammond, was sacked by the prime minister as party vice chairman in the aftermath of the vote.
Other EU member states could decide to move forward to trade talks with the UK at their two-day summit.
The negotiations are first expected to focus on agreeing a temporary arrangement that will kick in as soon as the UK leaves the EU in March 2019.