A good deal?

The Brexit deal maintains tariff-and quota-free trade with the EU, but the extra paperwork involved requires 50,000 more customs officers, according to an estimate by the UK government.

For Northern Ireland to continue abiding by single market rules to avoid a hard border with the Republic of Ireland, a virtual border is required in the Irish Sea.

Outside the EU, the UK can negotiate its own trade deals. To date, many of these closely resemble those agreed when it was a EU member state.

Discussing the most high-profile deal, with Japan, Minako Morita Jaeger, from the UK Trade Policy Observatory at the University of Sussex, said it was "almost identical" to the EU's existing terms with Japan and owed a debt to that deal.

"If the UK had had to negotiate with Japan from scratch, it would not have gained the level of market access that Japan accorded to the EU," she added.

The deal little involves the UK's financial services sector, which is worth $178 billion and supports 1.1 million jobs. This is because the EU wants to see what UK Chancellor of the Exchequer Rishi Sunak means by his country "doing things a bit differently" before deciding on the access allowed to its markets.

For years, fish have been used as bargaining chips. Under the Brexit deal, the two sides reached a compromise that will see European boats gradually transfer 25 percent of their current fishing rights to the UK fishing fleet during a transition period of five and a half years, rather than 80 percent over three years, as the government had sought.

The UK has agreed to the so-called level playing field for industry, so government support cannot be used to give British companies an unfair advantage. On immigration, the abolition of freedom of movement means EU citizens now face the same treatment in the UK as other overseas visitors. As a result, Britons' movement in the EU is now also restricted.

UK Home Secretary Priti Patel has said Brexit will make the country more secure.

However, the deal has seen the UK lose access to shared criminal intelligence data, including the Schengen Information System database.

According to a BBC report, the database was accessed about half a billion times every year by UK police, and the National Police Chiefs' Council said it was "essential for mainstream policing". However, Johnson has played down security concerns, saying, "I don't think people should have fears on that score."

The Brexit process has also resulted in a sizable pro-European lobby among former Remain supporters in the UK.

In 1971, Parliament debated for a week before voting to support the UK's membership of what was then the Common Market. Last year, it debated a four-year withdrawal process and 1,200-page document for less than one day.

Brexit has been, and may well continue to be, hugely divisive, but with the arrival of a new year, the result of the 2016 referendum has been delivered.

The Leave campaign won. Its supporters have their prize, and now it is time to open it. Nobody on either side knows exactly what lies within.