BBC
UK security chiefs have ordered an acceleration in police training to prepare for any future "Mumbai-style" gun attack in a public place.
A series of counter-terrorism exercises are being held with police marksmen training alongside units of the SAS.
Police armed response units are also being given more powerful weapons.
Recent intelligence had revealed the early stages of an al-Qaeda plot to carry out co-ordinated attacks in the UK, France and Germany.
They were planning to copy the 2008 attacks in the Indian city of Mumbai, where 10 gunmen went on a three-day rampage, killing 166 people and injuring more than 300.
The BBC's security correspondent Frank Gardner said the UK authorities had been planning for such an attack ever since Mumbai happened.
"David Cameron has taken a personal interest in the problem ever since his first threat assessment given to him when he took office in May.
"Now police armed response units are getting their firepower and their stocks of ammunition increased to deal with multiple terrorists armed with automatic weapons," our correspondent said.
A Whitehall official told the BBC that Metropolitan Police had not been asked to to do this before.
He added that the job of the police would be to contain such a situation while the job of the SAS (Special Air Service), if called upon, would be to resolve it.
Threat level
Former Security Minister Lord West told the BBC the police must be properly trained to deal with such terror attacks.
"These people like the Mumbai terrorists, are a bit like soldiers, they do fire and support, move forward, all they want to do is kill as many people as possible, with slightly heavier weapons than our police have," he said.
"And therefore you have to give heavy weapons to the police and train them how to do it.
"There is no way, except at immense cost, you could have SAS-level trained troops in every part of the country to be able to respond in the timescale you'd need. The police are there and have to do that first response."
Meanwhile, plans are being drawn up for an SAS unit to be stationed in London throughout the 2012 Olympics.
It emerged last month that jihadist fanatics were planning to replicate the Mumbai attacks in Europe.
Western intelligence sources said small teams of militants were planning to seize and kill hostages. It was also reported that recent US drone raids in Pakistan had been targeting the al-Qaeda militants who inspired the plans.
UK officials said the plot had not been stopped, but an attack was not expected to be carried out imminently.
The UK national threat remains at severe, where it has been since January, meaning a terrorist attack is thought highly likely.
