Britain prepares to launch Brexit

London : Britain will take an unprecedented step into the unknown on Wednesday with the first formal move towards leaving the European Union, starting a two-year process that has already divided the country.

Tens of thousands of people took to the streets of London on Saturday to protest against Brexit, and Scotland's parliament on Tuesday is set to vote in favour of holding an independence referendum.

Scots voted to stay in the EU but the majority verdict in Britain's EU referendum last year was 52 percent in favour of putting an end to a loveless marriage that has lasted more than four decades.

Those in favour are impatient for Brexit talks to begin and accuse Prime Minister Theresa May of playing for time since the June referendum.

But europhiles are increasingly concerned.

"Stop this madness!" read a banner held up at Saturday's march to parliament -- held just three days after a terror attack there -- to coincide with the 60th anniversary of the EU's founding treaty of Rome.

Prime Minister Theresa May's formal letter of notification to EU President Donald Tusk will trigger Article 50 of the EU's Lisbon Treaty: an exit clause that no member state has ever used.

The EU is expected to issue a first response later this week, followed by a summit of EU leaders on April 29 to adopt guidelines for the talks.

The exit negotiations themselves are not expected to start until at least three weeks after that.

The referendum campaign created bitter rifts between different parts of the country, generations and social classes, as well as exposing a chasm between the haves and have-nots of globalisation.

Brexit has also sparked a round of soul-searching in the European Union, even fears of a wider break-up.

EU leaders at a summit on Saturday adopted a declaration that enshrines for the first time a so-called "multi-speed" Europe, in which some countries can push ahead on key issues while others sit out.