The Queen has lit the National Millennium Beacon, triggering a string of beacons across the UK.

A trumpet fanfare sounded from Tower Bridge as she stepped forward to take the torch which ignited flames on a barge on the River Thames.

Within minutes of the Queen's actions, hundreds of beacons across England, Wales, Scotland and Northern Ireland were set alight to welcome the new century.

Earlier in the evening the Queen, en route to the Dome, stopped off at Southwark Cathedral for a service highlighting the religious significance of the millennium celebrations.

She also took time to meet some of the poorest people in society at a nearby homeless shelter.

It was left to UK Prime Minister Tony Blair to set London's millennium wheel in motion in another spectacular display.

He fired a laser beam across the Thames to officially open the new 450ft London Eye landmark.

It will spin slowly all night as the party continues around it - although there are no passengers on board after last-minute checks discovered that one of the 32 passenger capsules was unsafe.

The event was marked by deafening fireworks and a fly-past by British Airways' flagship jet, Concorde.

Before pressing the button Mr Blair said: "To everyone here and throughout Britain, have a happy and wonderful New Year.

"From us all here in Britain to people throughout the world, we wish you peace, we wish you prosperity in the new millennium."

Meanwhile police were preparing for up to four million party-goers in central London alone.

Crowds are thronging into the centre of London - which is to see the centrepiece of the UK's celebrations - with tens of thousands gathered in Trafalgar Square and the royal parks.

Thousands more are already gathering on bridges across the Thames ready for the midnight fireworks and pyrotechnic displays which will appear to set the river ablaze.

Culture Secretary Chris Smith said the government was prepared against any potential strike by the millennium bug.

"We're ready for anything that could happen - we've made all sort of emergency preparations but we hope none of them will be necessary," he said.

Scotland Yard have reported no major transport problems, although police decided to close central roads early to prevent traffic congestion as drivers tried to take their cars into the centre.

Blackfriars and Waterloo bridges have been closed. People are being warned to leave their cars at home and travel by public transport.

There are some 6,000 police on duty in central London alone. Home Secretary Jack Straw said he was confident forces would be able to cope.

The £758m Millennium Dome will be officially opened minutes before midnight by the Queen.

Highlights of the Dome programme include performances from the English National Opera Orchestra, music from Jools Holland, The Corrs and Mick Hucknall and prayers read by the Archbishop of Canterbury and three Barnardo's children.

But thousands of guests arrived to see in the new year after a day of frustration and fresh chaos over obtaining their tickets.

Many were forced to queue throughout the day for their passes at Stratford and Charlton railway stations after organisers failed to send them in time through the post.

The administrative fiasco then continued as guests, many of them in evening dress, suffered further delays while security checks were made before they were able to board special Jubilee Line trains to take them to the Dome at Greenwich.

London Transport bosses were at one stage forced to close Stratford station, in east London, after crowds waiting to travel to Greenwich swelled to dangerous levels.

In Scotland an estimated 180,000 revellers have packed into Edinburgh's streets to see in the New Year with Scotland's largest ever Hogmanay.

In Cardiff, a concert by Welsh band the Manic Street Preachers is the key event in Wales' millennium celebrations.

In Belfast and Londonderry huge crowds gathered for a night of musical festivities while in Omagh, where 29 people died in the August 1998 bomb, children lit a millennium beacon.

Around England, events range from a Cliff Richard concert in Birmingham to a lantern procession through the streets of Newcastle-upon-Tyne.