The European Union says it will not be "paralysed" after Britons voted to leave, but Brussels policymakers say uncertainty over Britain's future is already complicating the lawmaking process for the rest of the EU.
As London waits, possibly for months, for a successor to Prime Minister David Cameron to start negotiating an exit that will retain its easy access to EU markets, some Europeans fear that Britain could obstruct legislation to strengthen its hand.
"We cannot afford to be stuck in limbo. The British must not hold the EU to ransom," former Belgian premier Guy Verhofstadt told the European Parliament in a Brexit debate last week.
But despite his call, echoed across Brussels, for Britain to launch the two-year process of withdrawal, Mr Cameron has left that to whoever the party chooses to replace him in September.
Some frontrunners for Conservative leader say they see no hurry to trigger Article 50 of the EU treaty, the start of formal negotiations to leave the bloc, and some Britons want the referendum result reversed.
"It's slightly surreal," a British diplomat conceded, as EU leaders rule out any discussion of Brexit terms before Article 50 is live, so that EU officials and diplomats are in a vacuum.
One gag doing the rounds in Brussels recalls "Schrodinger's cat": as the physicist's imaginary pet was both alive and dead, so Britain is both in the EU and out, at the table but silent.
Britain is scheduled to chair ministerial councils for six months from next July.
But Mr Cameron has also left to a successor whether to go ahead with the presidency, irritating officials who reckon it takes two years to prepare a good agenda.
The official line from a British government spokesman is: "We remain a part of the EU until negotiations are concluded."
But British officials admit that on matters that will not affect Britain once it has left - most issues - they can have little say, leaving only short-term business - next year's EU fishing quotas, say - in which diplomats are speaking out.
"We are in a holding pattern," the British diplomat said.
Legally, British ministers retain full voting power in European councils, including a veto on some issues, and, in 751-seat EU parliament, Britain's 73 members keep voting.
But a Briton has already resigned a key parliamentary role on climate change, long an issue Britain has led on.
Legislation due this month to spread the burden of cutting carbon dioxide emissions could be held up, some officials say, while they rework the sums to exclude the bloc's second-biggest economy without knowing when, or even if, it will leave.
"We already feel we have lost credibility in the eyes of other MEPs," a UK parliamentary source said.
That Brexit has begun is evident in the European Commission, the EU executive, where British nominee Jonathan Hill resigned, costing London a key role overseeing financial regulation that was seen as helping the city against the eurozone.
Mr Cameron's successor can still nominate another commissioner, but cannot expect a major job; EU officials, stung by Britain's shock vote, sneer that London may get "commissioner for ballet".
At the level of summits of national leaders, too, Mr Cameron saw himself frozen out when the other 27 met on Wednesday in his absence.
For now, without Britain the European Council cannot make law, but such meetings will be common once London triggers Article 50, which keeps it out of negotiations with itself.