After Theresa May’s shocking defeat in the Commons last night as Tory rebels and opposition MPs backed an amendment giving them a legal guarantee of a vote on the final Brexit deal, the Prime Minister must now face her European counterparts in the last major EU summit of 2017.

After striking a Brexit divorce deal late last week, Mrs May will be hoping European leaders will back an agreement to move talks on to a second phase.

However, the summit comes at a time when Europe’s power balance is shifting. Angela Merkel, the German chancellor who has enjoyed almost unfettered dominance over the EU in recent years, has so far failed to form a coalition at home and is therefore heading to Brussels on the backfoot.

France appears to have usurped Germany as the EU’s main powerhouse, at least for the time being, and Emmanuel Macron arrives in Brussels in the knowledge that he can set the agenda for EU talks.

Ireland, meanwhile, has already been affected by Brexit talks after Theresa May, Irish Taoiseach Leo Varadkar and Northern Ireland’s DUP leader Arlene Foster finally broke the Irish border deadlock.

Mr Varadkar knows Ireland will be one of the member states most affected by Brexit and other EU countries are aware Dublin must be satisfied with the outcome of the summit for Brexit to move forward amid fears the delicate balance of peace could be threatened.

The voices of the Netherlands, Portugal, Italy and Spain all carry significant weight in Brussels, but these countries are split on the eurozone. 

Italy and Spain are backing France’s vision of a more integrated European economy, while Dutch prime minister Mark Rutte has already said “integration for integration’s sake” is not the answer.

Portugal will enjoy a bigger say in matters than usual given that its finance minister Mário Centeno, is now Eurogroup president, and the country is the Britain’s oldest ally.

Denmark and Sweden are likely to have more sway in Brexit talks than on economic reform because neither use the single currency.

Poland, Hungary and the Czech Republic have seen their relations with EU leaders sour over the course of the year and they are unlikely to have a big say in Brussels because none of them have any intention of joining the euro.

A number of smaller EU countries, particularly eastern members such as Croatia, Latvia and Romania, are unlikely to make a critical difference to Brexit talks or eurozone reform discussions - either because Brexit and the eurozone do not affect them or simply because their shares of the EU power balance are simply too small.