Thursday''s summit in Brussels will probably be the last time European leaders gather before British Prime Minister Theresa May formally invokes Article 50, the mechanism for leaving the European Union.

After speculation that May would take a formal letter to the summit, she now looks likely to arrive empty-handed.

But her defeat last week in the British Parliament's Upper House, which amended her bill on triggering Brexit, is only a minor setback that is unlikely to delay passage of the bill by more than a few days.

May still insists she is on track to trigger Article 50 by the end of the month, despite the defeat. Simon Usherwood, a political analyst at the University of Surrey, said the amendment made by the House of Lords was "not a very big setback".

"Once Article 50 is triggered, the initial stumbling blocks on the British side will be that it "still doesn''t really know what it wants," Usherwood said.

"The plans set out in Theresa May's speech and in the White Paper say we want a free trade agreement-plus, that we want to do lots of things, but we don't want to have the freedom of movement elements," he said.

"So it''s not a very clear plan: this very confusing language about special membership of the customs union, but not being part of the basic elements of the customs union; an unwillingness to be under the courts of justice jurisdiction, which will create additional problems.

"So at the moment the British position is very much about what they don't want, rather than about what they do want, so that will make it very hard for the EU 27 to engage," Usherwood said.

For their part the remaining 27 EU members will try to focus on business as usual, until they have received the official notification from Britain.

With election season in full swing in The Netherlands, France and Germany, Europe's leaders are keen to make some progress on the issues that might help them woo those voters, who have been charmed by anti-establishment populists.

EU economy in decent health

The state of the European economy presents a conundrum. While for the first time, in years, the Eurozone economy is in decent health, politicians are struggling to reap electoral rewards.

That's why the question of how the benefits of economic growth can be spread more widely and fairly among European citizens, will probably feature prominently on Thursday's agenda.

The same goes for the question of how to curb illegal migration to Europe.While a deal between Turkey and the EU managed to drastically reduce the number of refugees entering Europe through Turkey, there has been a steady number of arrivals in Italy, mainly from Libya but also via Egypt.

EU leaders are also likely to discuss the divisive question of relocation. In the run up to the summit the EU commissioner for migration, Dimitris Avramopoulos, criticised the lack of willingness by certain member states to take in their fair share of migrants.

"Responsibility cannot be fairly shared without solidarity. Member states cannot cherry-pick what they deliver on," Avramopoulos said.

He was referring to 160,000 people currently in Italy and in Greece, who have been identified as in need of international protection, and who are supposed to be relocated to other EU member states by September 2017.

According to the commissioner, so far only Malta and Finland are on track to meet their resettlement obligations, whereas Hungary, Austria and Poland are still refusing to participate in the scheme at all and others such the Czech Republic, Bulgaria, Croatia and Slovakia are doing so only on a very limited basis.

Britain's May is not expected to stay on in Brussels for the informal gathering of the other 27 EU leaders on Friday, when they will focus on the question of how to shape the European Union after Britain''s departure.

- dpa