Under plans being drawn up by Scotland Yard, armed police units will be on patrol around the clock in trouble spots in the capital.
The changes would see the Metropolitan Police's firearms unit, CO19, expanding from 700 to 900.
The unit attracted attention earlier this year after two of its officers were interviewed in relation to the shooting of the innocent Brazilian Jean Charles de Menezes at Stockwell Tube on 22 July.
There is growing pressure for more armed officers on Britain's streets, particularly with the threat of terrorist attacks. These latest plans are expected to be copied across the UK.
The association that represents rank and file police officers is also preparing to ask its members whether they would like to be armed, although successive chief constables and home secretaries have been against this.
The proposed increase follows an internal review at the Met. This was sparked partly by the shooting dead of PC Sharon Beshenivsky, an unarmed officer who was murdered after going to a robbery in Bradford in November.
Sir Ian Blair, the Met Commissioner, is also concerned about the continuing rise in gun crime, which rose by five per cent in the past year in London.
Assistant Commissioner Steve House, the head of the Met's central operations, which includes the firearms unit, said: "We don't want to go down the route of a totally armed service. We want firearms officers to be specialists. We are looking to see whether it should expand to a permanent armed presence in the boroughs."
He stressed that no final decision had been made, but said: "My view is that the right way to go is to increase CO19 further, then have armed officers in boroughs. It's the sensible thing to do."
Gun crime in London has increased by 5.3 per cent - up 195 offences to 3,903 - in the year up to November 2005 compared to the same period in 2004.
The latest figures for Operation Trident - the Met's operation against black-on-black gun violence in London - has shown a 34 per cent rise, from 108 offences to 164 in the six months from April to October 2005, compared with the same period last year.Reuse content