Theresa May is holding last-minute Brexit talks with the leaders of Germany, and France later, with the UK due to leave the EU in three days time.
Mrs. May is meeting Angela Merkel in Berlin, followed by Emmanuel Macron in Paris, to urge them to back her request to delay Brexit again until 30 June.
The prime minister will be at an emergency summit on Wednesday when all EU states will vote on an extension.
Cross-party talks aimed at breaking the impasse are also set to continue.
The negotiating teams will be joined by Chancellor Philip Hammond, Environment Secretary Michael Gove, and shadow chancellor John McDonnell, with the Labour frontbencher saying they hoped to “broaden the talks”.
But in a leaked letter seen by the Telegraph, International Trade Secretary Liam Fox has warned that agreeing with Labour over its demand for a customs union is the “worst of both worlds” and will leave Britain unable to set its own trade policy.
The UK is currently due to leave the EU at 23:00 BST on Friday.
So far, MPs have rejected the withdrawal agreement Theresa May reached with other European leaders last year.
One of the most contentious parts of the plan is the Irish backstop – an insurance policy that aims to prevent a hard border returning to the island of Ireland.
The EU has continually said it will not re-open the withdrawal agreement for negotiations, but Leader of the Commons Andrea Leadsom renewed her plea for them to look again.