David Cameron is to meet European Union leaders for the first time since the UK voted to leave.
The UK prime minister will discuss the implications of the Brexit vote and the way ahead at an EU summit in Brussels.
German, French and Italian leaders said on Monday there could be no "formal or informal" talks on a British exit at this stage.
Meanwhile, Health Secretary Jeremy Hunt has called for a second referendum over the terms of the UK's departure.
He said the withdrawal process should be delayed until shortly before the next election - meaning a delay until after 2022 at the earliest.
He is the first cabinet minister to go public with the call.
Mr Hunt, who is considering standing for the leadership after Mr Cameron stands down, said the UK must remain within the EU's single market.
He floated the idea of a "Norway plus" arrangement outside the EU, where the UK would enjoy the current trade benefits of being a full EU member while negotiating revised immigration rules.
The British public's concerns about immigration needed to be addressed, he said, and that was also in the EU's interest as it "faced collapse" unless the current right of all citizens to live and work in other member states was reconsidered.
In other developments on Tuesday, Chancellor George Osborne ruled himself out of replacing Mr Cameron as prime minister.
He said in the Times that he had fought hard for a vote for remaining in the EU, and though he accepted the referendum result "I am not the person to provide the unity my party needs at this time."
Labour MPs will vote on a motion of no confidence in their leader Jeremy Corbyn - who has insisted he is staying put - while Scottish First Minister Nicola Sturgeon will address MSPs over Brexit's implications for Scotland's future.
As Europe tries to come to terms with Britain's decision to leave, Mr Cameron will attend a working dinner of EU leaders after meetings with European Council President Donald Tusk and European Commission President Jean-Claude Juncker.
He will not attend talks between the leaders of the other 27 EU member states at breakfast on Wednesday.
'Swift and coherent'
Speaking on Monday, Mr Cameron said the UK must accept the referendum result and that a special unit within government was being set up to lay the initial groundwork for leaving the EU
