A police support unit from Sussex was reported to be in East London early in the evening.
The unit consists of three vehicles each with a sergeant and six constables – and an inspector in overall charge.
In a statement a spokesman for the force said: “Sussex Police has sent a small number of officers specially trained in public order policing to London this evening.
“This is part of routine mutual aid agreements between forces under which assistance can be given to help police large incidents.
“Policing continues as normal across Sussex and any requests for support are assessed considering the need to maintain local policing.”
Further requests were believed to have been made during the evening and were being considered. The BBC also reported that the Sussex and Surrey police helicopter had been called in to provide help.
A number of companies allowed staff who commute in from places like Brighton and Hove to leave early this evening as rumours about further trouble gathered pace on Twitter.
Later in the evening Southern, the train company, advised passengers not to travel to South London. The expectation was that commuters would be safe to travel in the morning (Tuesday 9 August).
Many shops around East Croydon and West Croydon railway stations closed early today and during the evening television news bulletins have been showing aerial pictures of fires in the area.
Some damage was also reported to shops close to Clapham Junction railway station, with Sky TV showing pictures of looting to the noise of burglar alarms wailing in the background.
Among the shops in Clapham to have been ransacked was a branch of Currys. The Waterstone’s bookshop next door was untouched.