Thousands of hardy revellers have braved chilly temperatures to see in the new year.
In central London, crowds lined the banks of the River Thames to witness the city's annual fireworks display.
Supt Brian Pearce, of the Metropolitan Police, said people had heeded warnings to arrive early to get a good view of the show to welcome 2009.
There were also giant projections and light shows on the walls of the city's landmark buildings.
The London Ambulance Service said there were fewer calls in the first hour of 2009 than in 2008 - down from 377 to 292. Police had made 78 arrests.
In Edinburgh, there was a mass rendition of Auld Lang Syne after the chimes sounded. Fireworks lit up the night sky. Organisers said it was the world's biggest rendition of the Robert Burns' poem, which commemorated the 250th anniversary of the Scottish poet's birth.
Earlier, about 9,000 music lovers had been treated to sets from Scottish singer Paolo Nutini and dance act Groove Armada at the sell-out Concert In The Gardens event.
Rockers Glasvegas and electropop group Hot Chip were also performing on other stages in the city.
The creative director of Edinburgh's Hogmanay, Pete Irvine, said there had been a slower uptake of tickets than usual this year, but a "big rush at the end" made sure the event was a sell-out.
Police said Edinburgh's street party had been a successful and safe event, with a well-behaved crowd and only three arrests for breach of the peace.
