Talks over the potential use of water cannon for the first time on London's streets are taking place with the Metropolitan police, the Home Office confirmed on Monday.
London's police force argue that water cannon would be a "valuable option in rare situations" and press reports suggest that Home Office ministers broadly back the measure.
But police declined to comment on media reports that they were pushing for them to be bought ahead of June's G8 summit to be held in Northern Ireland, with anti-capitalist protests already planned in London.
Water cannon have long been used in Northern Ireland policing - particularly during sectarian clashes between Protestants and Catholics - but have yet to be deployed on the British mainland.
London police want to buy two German-made water cannon vehicles at a cost of 1.3 million pounds each, acccording to The Times newspaper.
Leaders representing the world's biggest economies are meeting near the Northern Irish town of Enniskillen next month, where a bomb was defused by police in March.
The Met police can have access to Northern Ireland's water cannons within 24 hours but decided not to use them during the Summer rioting in many British cities two years ago.
In the worst civil unrest for a generation, homes and businesses were burnt in August 2011, sparked by the shooting of a man in north London.
But a 2012 police review of the riots said water cannon would not have been "an appropriate and practical option" due to the speed and agility of those involved in the disorder.
The Home Office confirmed it was "providing advice to ... the Metropolitan Police on the authorisation process for the use of water cannon."