London mayor Sadiq Khan is to make an "emotional" case for the EU to cut a fair Brexit deal with the UK as he delivers a keynote speech in Brussels.
Mr Khan will use the address to stress that London will remain Europe's only global city after withdrawal, and that both sides need each other to boost their own prosperity.
The London mayor is to emphasise the potential for the EU and the UK if the two take a mutually beneficial approach to Brexit.
Mr Khan will also stress the emotional bonds the UK has with its European neighbours as he challenges Prime Minister Theresa May to guarantee the status of 3.3 million EU nationals living in Britain when she formally triggers Article 50 and officially launches Brexit on Wednesday.
Mr Khan's speech will be followed by a string of high-level meetings intended to push the message that London wants EU trade and investment after Brexit.
The mayor will have a series of talks with Jean-Claude Juncker, president of the European Commission, European Parliament president Antonio Tajani, and the European Parliament's Brexit negotiator, Guy Verhofstadt.
Mr Khan was trying to reschedule a meeting with European Council president Donald Tusk after "unforeseen circumstances" saw talks cancelled on Monday.
The mayor will then travel to Paris to launch an air quality initiative with his counterpart in the French capital. Mr Khan will also hold talks with the French interior minister after the Westminster attack.
The move comes after the EU's security commissioner, Sir Julian King, said the atrocity in London showed that Europe needs to "work together" to counter terrorism.