As the British electorate votes in the most important referendum for a generation, across the channel EU officials are nervously awaiting a result that could have devastating consequences for the EU.
While there has been a reluctance to draw up a written contingency plan for Brexit amid concerns that it could be leaked to the media, contingency discussions have been quietly taking place in Brussels.
Diplomats from the EU's largest states, including France and Germany but excluding Britain, met senior European Commission officials in Brussels last month to discuss formally the possibility of Brexit. Discussions have been ongoing in parallel in national capitals.
According to one official, co-ordinating a response between the EU institutions and member states will be a crucial element of the official response tomorrow.
With the final result expected at around 7am tomorrow, a meeting between European Commission president Jean-Claude Juncker, the head of the European Council Donald Tusk, European Parliament president Martin Schulz and Dutch prime minister Mark Rutte, holder of the EU presidency, has been scheduled for 10.30am in European Commission headquarters in Brussels.
In Frankfurt, the European Central Bank is expected to respond to the result in close consultation with Brussels, with members of the bank's governing council on standby for a conference call.
Should Britain vote to leave an ECB statement is expected early tomorrow morning in order to calm markets amid concerns about a contagion effect on euro zone countries, particularly Ireland, which officials believe is particularly exposed.
Intensive meetings
Should Britain vote to leave the EU intensive meetings are expected to take place throughout the weekend at the European Commission’s headquarters in Brussels involving EU ambassadors, commissioners and officials ahead of the reopening of financial markets on Monday.
Similarly, MEPs have been told to prepare for an emergency plenary session in Brussels next week should Britain vote to leave.
A summit of EU leaders, including British prime minister David Cameron, is scheduled for next Tuesday and Wednesday in Brussels, having been postponed due to the British referendum.
While a British exit from the EU would present an existential crisis for the European project and open an unprecedented legal and administrative minefield, it will also have a more immediate impact on the lives of thousands.
Since the announcement of a planned referendum last year, British nationals living and working in Brussels have been nervously assessing their future.
Almost 1,200 British nationals work for the European Commission, with thousands more employed in other EU institutions such as the European Parliament, European Council and the European Court of Justice in Luxembourg.
In addition, hundreds of Britons work for the many international organisations and non-governmental organisations that are based in Brussels.
Yesterday a memorial event was held for the late Jo Cox MP at a concert hall in central Brussels. Like many young British nationals, she spent some of her working life in Brussels, working for British MEP Glenys Kinnock and later for Oxfam.
Under EU treaties those working for the EU must be a national of a member state. This means that a British exit from the EU would theoretically mean that British officials would be out of a job.
Promotion
In reality, there is an expectation that those already employed by the EU will retain their positions. Nonetheless, British EU personnel have expressed concern privately that their chances of promotion would be jeopardised in the event of Brexit.
Many have spent the last few months seeking a second passport or dual nationality, with some utilising their Irish heritage to apply for Irish citizenship through the Irish Embassy in Belgium. Others are seeking naturalisation as Belgian citizens.
Tonight members of the British ex-pat community – many of whom have lost the right to vote as they have lived more than 15 years outside the country – will gather in Place Luxembourg outside the European Parliament in Brussels or in one of the many bars near the European Commission’s headquarters in the Schuman area of the city.
For these individuals a British exit could have very real and immediate consequences.
But right across the EU a British exit will have unprecedented repercussions.
Tomorrow morning the European Union’s 500 million citizens may be waking up to a very different world.