Brexit supporters have been given permission for a party in London’s Parliament Square at the moment the UK leaves the EU on 31 January.
The event, being organised by Leave Means Leave, is due to take place between 21:00 and 23:15 GMT.
The UK will leave the EU at 23:00 GMT, 47 years after it joined the then European Economic Community in 1973.
Veteran Brexit campaigner Nigel Farage said it was “a big moment in the history of this nation to celebrate”.
The Office of the London Mayor said “provisional authorisation” had been given for the event.
It is understood the campaign group has been asked to provide assurances about the time it will take to clear the site after the event before final authorisation is given.
The government is looking at ways of marking the UK’s historic departure from the EU.
Boris Johnson has said he supports a crowd funding campaign to allow Big Ben to chime at 23:00 GMT.
The Elizabeth Tower, which houses the bell, is currently being refurbished and Big Ben is only chiming twice a year, on New Year’s Eve and Remembrance Sunday.
The parliamentary authorities have raised concerns about the cost to the taxpayer of bringing it back into use for a few minutes. The House of Commons Commission said it could cost up to £500,000 and MPs would need to explicitly approve such expenditure.
Mr Farage told LBC that if Big Ben did not chime at 23:00 on 31 January, “our country is going to look like a joke.”
Leave Means Leave has launched a website to promote the event, in which people can sign up for details.
Brexit Party chairman and MEP Richard Tice suggested it had even bigger plans.
Other MPs have called for church bells to ring out at the moment of exit. Former Tory leader Iain Duncan Smith told the BBC that he would love this to happen but it was a matter for individual churches rather than politicians.
However, others have warned about overly “triumphalistic” celebrations following years of political acrimony and division over the issue.
Speaking in Parliament on Tuesday, Lib Dem peer Lord Greaves said Brexit represented a “bereavement” for the three million EU nationals living in the UK and jubilant festivals would make matters worse for them.
He warned of the risk of EU nationals being targeted by a “hostile minority” and that “some things may happen in some places which could be reminiscent of things happening in Germany in the early 1930s”.