After three-and-a-half years of high drama, "Brexit Day" was ushered in on both sides of the Channel with jubilation, anger, sad vigils and sham marriages - and indifference from those who just don't care any more.

London/Brussels (dpa) - With the final countdown to Brexit approaching fast in London, the crowds in Parliament Square who came to mark the event that has driven British politics for more than three years were smaller than expected.

For the first time in the European Union's history, the bloc will lose a member when Britain leaves at 11 pm (2300 GMT).

The tussling over Brexit laid waste to dozens of political careers and left Britain divided, polarized and more than a tad jaded.

For Brexiteers gearing up for celebrations in London later Friday, it's a happy day.

Richard English, an Englishman in his 50s carrying a large British Union Jack flag in Parliament Square, said he was among the 52 per cent who voted to leave the EU in the 2016 Brexit referendum.

'[I have] nothing against the EU itself," English told dpa. "It's just I believe the EU is corrupt and undemocratic. You can't vote for presidents and things like that, and the law-making is one-sided to the sovereign nations."

"So hopefully we'll move away from that and make our own rules, do our own free-trade agreements," he said.

"So then we can prosper, basically. We haven't had that for 47 years, so hopefully we'll grow as a nation."

Hundreds of people gathered in the square ahead a celebration scheduled to feature music and speeches by Brexiteers, including former UK Independence Party leader Nigel Faraqe.

Some Brexiteers chanted "Bye bye EU, bye bye" and "We're coming out," and sang the patriotic anthem "Rule Britannia."

Others carried English, British and US flags, with banners and T-shirts bearing messages including, "Brexit - Free at last" and "Let's go WTO."

Less pleased was Silvia Zamperini, an Italian native who has lived in Britain for 26 of her 51 years: "Brexit is a disaster. Many British people are now racist, homophobic and intolerant."

On the other side of the Channel in Brussels, triumphant Brexit party representatives left the European Parliament for the last time on Friday morning in procession, holding a Union Jack.

To the rousing sound of bagpipes and with cries of "Brexit!" they set off to board the Eurostar train to London, where many were expected to join the festivities.

The British capital also saw anti-Brexit protesters unfurling a banner reading "Here to stay, here to fight! Migrants in, Tories out!" on Westminster Bridge in the early afternoon.

On Thursday night in Brussels, outgoing British EU lawmaker Magid Magid held an anti-Brexit party complete with a balloon-covered arch for "sham marriages" on a muddy square opposite the European Parliament.

EU citizens could "marry" Brits under the Green party politician's supervision.

"There's a lot of Brits that want to stay in Europe so we thought we maybe could find some suitable partners," he told dpa with a smile despite the drizzling rain.

The EU institutions played Friday more low-key, mostly refusing to say when British flags in their buildings will be lowered.

The 28th EU flag outside the European Commission building will be left in place, a spokesman told dpa.

In Northern Ireland, which has been at the centre of Brexit negotiations because of its border with EU member country Ireland, activisits from the pro-British Unionist community planned to mark the day of Britain's EU departure from outside the territory's devolved assembly.

Brexit is particularly unpopular in Northern Ireland and Scotland, where majorities voted to remain in the EU in 2016.

Leaders of Irish republican party Sinn Fein erected a billboard at Irish-Northern Ireland border with a message saying "Brexit: The fight goes on" early Friday.

"We did not consent to Brexit. It's time for Irish Unity - it's our route back to Europe," Sinn Fein tweeted with a photograph of the protest.

In Edinburgh, the Scottish capital, a "Missing EU already" event with music and a light show was planned on Friday night, including "a time for reflection plus anthem singing" in the final Brexit hour.

Scotland's devolved government has encouraged people to hold candelit vigils asking Brussels to "Leave a light on for Scotland."

Despite the festivities and commiserations, little will change in practice until the Brexit transition period runs out at the end of the year.

For most people, January 31 is a day like any other. Belgian-British dual national Richard Wells attended an event at Brussels' Grand Place town square on Thursday, but isn't planning much to mark the stroke of midnight (2300 GMT) on Friday.

"I'm just going to spend it quietly at home, with a few drinks," the long-term Belgian resident says. "Probably, champagne. And then we'll sit back and see how they handle the mess they've made."