Meanwhile Theresa May is heading to Brussels for an EU summit, less than 24 hours after surviving a vote of confidence.
The prime minister is seeking legally binding pledges from EU leaders on the Irish backstop – a key obstacle for MPs who oppose her Brexit deal.
The EU will not renegotiate the deal but may be willing to give greater assurances on the temporary nature of the backstop.
The secret ballot was triggered by 48 of her MPs angry at her Brexit policy, which they say betrays the 2016 referendum result.