British police said they would temporarily close roads around Queen Elizabeth's London residence Buckingham Palace during a military ceremony on Wednesday, bringing forward plans to do so in response to a truck attack in Berlin.

London's Metropolitan Police said that they would trial a two-hour road closure plan for three months to protect the large crowds that gather on days when the Changing of the Guard ceremony is held outside Buckingham Palace.

The road closures started earlier than had been planned by security chiefs due to the attack in Berlin on Monday, when a truck ploughed into crowds at a Christmas market, killing 12 people and injuring 48.

"The road closures, which have been planned for some time, are a precautionary measure and not in relation to any specific intelligence," the police said.

Britain is on its second highest threat level, meaning an attack by militants is considered highly likely. Earlier this month, Britain's foreign intelligence chief said Islamic State militants were using turmoil in Syria to plot attacks against the United Kingdom and her allies.