A new era has begun for the United Kingdom after it completed its formal separation from the European Union.

The UK stopped following EU rules at 23:00 GMT, as replacement arrangements for travel, trade, immigration and security co-operation came into force.

Boris Johnson said the UK had "freedom in our hands" and the ability to do things "differently and better" now the long Brexit process was over.

But opponents of leaving the EU maintain the country will be worse off.

Scottish First Minister Nicola Sturgeon, whose ambition it is to take an independent Scotland back into the EU, tweeted: "Scotland will be back soon, Europe. Keep the light on."

BBC Europe editor Katya Adler said there was a sense of relief in Brussels that the Brexit process was over, "but there is regret still at Brexit itself".

The first lorries arriving at the borders entered the UK and EU without delay.

On Friday evening, Transport Secretary Grant Shapps tweeted that border traffic had been "low due to [the] bank holiday" but there had been no disruption in Kent as "hundreds" of lorries crossed the Channel with a "small" number turned back.

Six freight loads travelling from Holyhead in Wales to Ireland had to be turned away due to not having the correct paperwork, the Stena Line ferry and port group said on Friday morning.

But later on Friday, the group said freight traffic was flowing well through its ports and government customs systems were working well.

It added that the fall in freight traffic after the Christmas and Brexit stockpiling period meant "it is too early to draw any conclusions", but the company remained "cautiously optimistic that, as freight volumes begin to rise again, we will be able to ensure the continued free movement of goods".

UK ministers have warned there will be some disruption in the coming days and weeks, as new rules bed in and British firms come to terms with the changes.

But officials have insisted new border systems are "ready to go".

As the first customs checks were completed after midnight, Eurotunnel spokesman John Keefe said: "It all went fine, everything's running just as it was before 11pm."

Northern Ireland has different arrangements from other parts of the UK, meaning there will be some customs checks on goods moving between Great Britain and the province.

On Friday afternoon, the first ferry from Great Britain operating under the terms of Northern Ireland trading protocol docked in Belfast, on schedule at 13:45 GMT.

Seamus Leheny, policy manager at Logistics UK, said six out of the 15 lorries that were on the first ship to arrive into Belfast were brought in for inspection, with one being kept at the port for more than three hours.

"Inevitably there are going to be teething problems because with such a new, complex system as this there are going to be issues in the first few days," he told BBC Radio 4's PM programme.