A brave new world or a dangerous leap into the unknown? After nearly 50 years of integration with Europe, Britain starts an uncertain new chapter on January 1.

Britain formally quit the European Union in January 2020 but has continued to observe all its rules during a transition period.

That half-way house ended at 2300 GMT on December 31. So from 2021, it will stand on its own, for better or worse.

A new trade deal, agreed after months of hard-fought talks and signed only this week, will smooth the path by lifting the prospect of tariffs and quotas for cross-Channel goods, from cars to lamb.

Without a deal, imports and exports would have faced serious disruption with the abrupt return of barriers that have not existed for decades.

There were fears that certain foodstuffs and medicines could run short.

Britain got a glimpse of what that might look like when France shut its borders to freight in response to the discovery of a new variant of the coronavirus.

But even with a deal, the future won't be seamless.

UK exporters will still need to file reams of new customs paperwork to prove their goods have authorisation to enter the EU's single market.

Britain has urged business to be ready either way, but industry players say the government has failed to deliver vital IT systems and support staff in time, heightening the risk of trouble after January 1.

Brexiteers argue the EU has held Britain back through onerous regulation and it can now embark on a buccaneering new mission to support free trade around the world.

Brexiteers claims the EU has held Britain back through onerous regulation
Brexiteers claims the EU has held Britain back through onerous regulation POOL / TOBY MELVILLE

That mission taps into Britain's seafaring roots as a great power and amounts to "God's diplomacy", according to a February speech by Prime Minister Boris Johnson.

But if heaven was listening, it had other plans in mind: a month after Johnson's speech, Britain was forced into national lockdown by the coronavirus pandemic.

If the world ever gets back to normality, the idea is that Britain will not shrink inwards after Brexit but will look outwards, as far afield as a free-trade pact with Pacific Rim countries.

"Now Global Britain is back, it is time for the makers, the doers and the innovators to help us write our most exciting chapter yet," International Trade Secretary Liz Truss declared in October, touting UK exports of everything from clotted cream to robots.

Truss has already signed a post-Brexit trade deal with Canada, Japan, Singapore and Switzerland, among others.

It is also eyeing a deal with India, and negotiating others with the United States, Australia and New Zealand -- Britain's partners in the "Five Eyes" collective of English-speaking intelligence powers.

Further deals in the pipeline will cover 80 percent of overseas trade by 2022, according to the government, which has shaken up the Foreign Office to integrate aid and development into Britain's diplomatic agenda.

Johnson's pitch to voters in last December's general election was to "get Brexit done" and focus both money and attention on parts of the country that have failed to benefit from London's finance-driven growth.

That "levelling up" agenda to bring new investment such as high-speed rail to northern England has been all but side-tracked by the pandemic.

But the government insists its long-term goals remain in place and that membership dues sent to the EU will be better spent at home.

Some Brexiteers want a radical overhaul of Britain's economic model, to turn the country into "Singapore on Thames" -- a lightly regulated, lightly taxed rival to supposedly sclerotic Europe.

Yet the government stresses that any free-trade deals won't sacrifice its "red lines": the state-run National Health Service, food standards and UK farming.

All of those sacred cows could be carved up if the United States forces post-Brexit Britain to yield to the same kind of concessions on trade that the world's most powerful economy has negotiated elsewhere.

With Joe Biden preparing to take office as US president, Johnson has already ceded some ground by agreeing to keep Northern Ireland largely in the EU's regulatory orbit after January 1, unlike the rest of the UK.