Thousands of police watched over New Year revellers as the night sky above London was illuminated by a spectacular fireworks display.
Crowds gathered on the banks of the Thames and in city centres across the UK to see the start of 2016.
Around 3,000 officers were deployed across central London, including firearms police, at a time of heightened global security in the wake of the Paris terror attacks.
Tens of thousands lined banks and bridges along the Thames, braving intermittent spells of rain ahead of a midnight display featuring around 12,000 fireworks which produced 50,000 projectiles.
The celebrations went ahead as planned, despite a similar display in Brussels being cancelled due to safety concerns and German authorities warning of a "serious imminent threat" at an event in Munich.
Two railway stations in the Bavarian city were evacuated after police were tipped off by a foreign intelligence service that Islamic State (IS) was planning attacks with five to seven suicide bombers, according to German media.
The Edinburgh Hogmanay also saw several firework displays above the city's castle, as well as a performance from Scottish rockers Biffy Clyro.
In Dubai, the New Year celebrations were tempered by a huge blaze in one of its tallest buildings.
The arrival of the New Year was greeted by silence in Moscow - the fireworks display was five minutes late.
The Met confirmed New Year's Eve was one of two events - along with Notting Hill Carnival - in which there was no holiday entitlement, meaning all available staff were called upon.
The force said it had worked closely with the mayor's office, British Transport Police (BTP), Westminster City Council and others to ensure the event ran smoothly.
There were a total of 48 arrests overnight, including four for drug possession, three for carrying offensive or bladed weapons and five for assaults on police officers.
Six people were also detained for public order offences, 11 for assault and one for sexual assault, the Met said.
The mayor's fireworks display was ticketed for the second year and was sold out.
Met spokeswoman Superintendent Jo Edwards said the extra officers were for reassurance and the event was "successful".
She said: "Our officers worked alongside stewards to support their operation and help people to get in and out of the event area safely and efficiently.
"Although the celebrations have drawn to a close, officers continue to work through the night to facilitate the clean up operation and bring the area back to normality in time for the New Year's Day parade."
Today, more than 8,500 performers representing 20 countries will take part in the annual New Year's Day parade through London, again amid a large security operation.
The event, which includes marching bands, cheerleaders, clowns and acrobats, kicks off in Piccadilly and finishes in Parliament Square, taking in Lower Regent Street, Pall Mall, Trafalgar Square and Whitehall.