New year celebrations: Revellers gather in London and across UK
Thousands of people have gathered across the UK to watch New Year's Eve fireworks to herald the start of 2015.
Some 100,000 revellers lined the River Thames in London for the first ticketed new year's display.
Huge crowds also took to the streets in Edinburgh and across Scotland for Hogmanay celebrations.
Celebrations were held across the world with fireworks displays in a host of major cities.
Shortly after midnight, Prime Minister David Cameron tweeted: "Happy New Year."
In London, a crew of more than 300 set off 12,000 fireworks as part of the annual display.
The display was counted in by a 10-minute digital countdown on the western facade of The Shard - the central London skyscraper - followed by lighting comprised of searchlights, strobes and a 2015 numeric graphic.
It was the first time the display has been ticketed, with revellers paying £10 to cover the costs of running the display.
It comes after an estimated 500,000 people tried to see the 2013-14 new year display, resulting in many being turned away for safety reasons.
Mayor of London Boris Johnson tweeted: "London's dazzling fireworks were a wonderful way to welcome in the New Year. Thanks to all who made it such a safe & fun event."
The Metropolitan Police said that by 06:00 GMT 90 people had been arrested in London, including 27 for being drunk and disorderly, 22 for assault, seven for sexual offences, six for drugs offences and two for possession of an offensive weapon.
The force said 4,000 officers had been part of the policing operation, while London Ambulance Service operations director Jason Killens said paramedics had also had a busy night.
"We're taking an emergency call every 10 seconds and we are expecting it to get even busier," he tweeted.
Elsewhere, West Midlands Ambulance Service said it had received more than 100 calls within the first 30 minutes of 2015, adding that "quite a few are alcohol related".
A spokesman said that between 20:00 GMT on New Year's Eve and 04:00 GMT on New Year's Day, handlers responded to 1,436,999 calls.
East Midlands Ambulance Service tweeted: "We've had over 340 calls in 1st two hrs. That's a new call every 21 secs!"
Edinburgh hosted an estimated 75,000 people at its Hogmanay street party and fireworks display.
Events were also held in Aberdeen, Inverness, Stirling and Stonehaven, while a warm-up party was held in Glasgow.
However, Hogmanay celebrations on Stirling Castle's esplanade had to be cancelled owing to high winds.