Brussels - Brexit and the departure of Britain's MEPs on January 31 will shake up the balance of power in the European Parliament and could complicate Brussels' reform agenda.

On paper, the main winner in the shake-up is European Commission president Ursula von der Leyen's centre-right European Peoples Party (EPP), already the biggest bloc.

But to pass her ambitious Green Deal programme intact and control the legislative process, the German conservative relies on a broad centrist coalition.

And here, things could get more complicated.

After the divorce, the assembly, which sits in Brussels and Strasbourg, will lose 73 British members, one of whom had already left last year to take up a seat in Britain's national parliament in Westminster.

The composition of the European Parliament after Brexit

- Greens slide -

Of these seats, 46 will be saved for representatives from any future new EU member states, but 27 will be immediately assigned to substitute candidates from existing states.

These were candidates from countries seen as under-represented in last May's election, and they have been waiting in the wings for their British colleagues to go.

The centre-right EPP doesn't lose any seats -- the British Conservative MEPs sat with a much smaller eurosceptic bloc -- and gains five from the new influx, swelling to 187.

The parliament as a whole will henceforth seat 705 MEPs. So von der Leyen would still be short of a 353-seat majority if she had to rely only on her EPP comrades.

The Brexit Party of Nigel Farage leaves with 27 seats. But he was not able to join any parliamentary group after the last elections and so this simply reduces the number of independents.

"No-one will miss them," said leading liberal MEP and former Belgian premier Guy Verhofstadt, whose own Renew group is hit by the departures of 17 UK Liberal Democrats.

Emotional final week for British MEPs as Brexit looms

- Orban out? -

The liberals remain the third force in parliament still behind the socialist S&D, which lost 10 British Labour Party MEPs but gain four new arrivals, leaving them on 148.

The far-right Identity and Democracy group gains strength with three new members to 76 and passes the Greens, who fall to 67 and to fifth place.

The eurosceptic ECR, minus its British Conservatives, is the sixth force on 59 seats, ahead of the radical left GUE on 40.

The 27 new members hail from France and Spain with five each, Italy and the Netherlands on three and two Irish.

To these are added a Pole, a Romanian, a Swede, and Austrian, a Croat, a Dane, a Finn, an Estonian and a Slovak.

So far, 15 of the newcomers have no obvious ideological home, and the Greens are hoping to make up their losses by recruiting several independents.

What are the main functions of the European Parliament?

- Five Star opportunity? -

They are eyeing three Catalan separatists -- despite Spain's efforts to have them stripped of their parliamentary immunity and sent home to face trial on sedition charges.

And they are also reaching out to Italy's anti-establishment populists in the Five Star Movement, which is losing ground at home to the far-right.

It would make for a very broad church party, and group co-president Philippe Lamberts admitted to AFP that the Greens are divided on the issue.

"Some want to work with whatever they can find to rebuild a fourth-place group, others want to wait. The group will take a position in the next few weeks," he said.

The liberals are also interested in Five Star, but already fell out in the last legislature.

If the smaller groups decide to take their time, they could see yet another upheaval even after the Brits have gone.

The EPP will decide on February 3 whether or not to formally exclude Hungarian Prime Minister Viktor Orban's Fidesz Party from its ranks over his assault on EU democratic norms.

This would cost them 14 seats and Orban might try to found a new right-wing populist faction, even if EPP officials say he is short of finding the 25 members for a formal group.

By Christian Spillman