Terrorist lorry attacks on crowds in Nice and Berlin this year forced UK police to "adjust" plans for protecting New Year's revellers, a senior officer said.

Armed police will join around 3,000 officers on the streets of the capital on Saturday as hundreds of thousands of people flock to watch the Mayor's firework display.

Concerns about the threat of a mass-casualty terror plot targeting the spectacle have been heightened after extremists struck busy public events in Europe.

In July, a lorry ploughed down the packed seafront promenade in Nice during the annual Bastille Day celebrations, killing 86 people and injuring hundreds of others.

A Christmas market in the heart of Berlin was the scene of a similar atrocity in December, when 12 people died as a truck packed with steel was driven into crowds.

But the Metropolitan Police's Detective Superintendent Phil Langworthy sought to reassure the public, saying there were "both over and covert" measures in place for protection.

He told the Press Association: "Clearly we have been looking at what has happened around the world in terms of Berlin, Nice, etcetera, and have adjusted our plans and continue to adjust our plans.

"We police around 3,500 large events every year including New Year's Eve and we meticulously plan those events - we have meticulously planned New Year's Eve - and we look at our tactics and we look around the world and adjust our tactics if need be.

"We have a very extensive planning period, we plan for many months, pretty much we start planning since the last event."

He added there was "no specific intelligence" for an attack on the end-of-year event, but said: "I would encourage people on the night if they see anything suspicious or have any concerns to come and speak to one of the police officers or stewards who will be on duty."

Huge numbers are expected to ring in the new year on the banks of the River Thames, but partygoers are likely to flood into other parts of central London, including major tourist spots such as Trafalgar Square.

Police urged those who did not have tickets for the set piece firework display, which has again sold out, to watch it from home instead.

Road closures will be put into place from 2pm on December 31, affecting Lambeth, Westminster, Waterloo and Blackfriars bridges.