Detectives were investigating whether the letter had been sent by an anti-facist organisation or whether it was the work of a competing
faction within the National Front.
The post had been collected from a PO box at a nearby post office. It was not clear if anyone else was in the house.
Residents said the emergency services and a fire engine had been called to the house. Mr Anderson was treated at Newham General Hospital and later released.
As details of the incident emerged, residents voiced fears that it would herald clashes between ultra right-wingers and anti-facists.
Pensioner Hetty Tellis, who lives opposite, said: 'It's very frightening that sort of thing happening right next door.'
Another neighbour, who refused to be named, said Mr Anderson had been the target of attacks before. He said: 'About a year ago someone tried to blow his car up. It went off and there was a little fire around his front wheel.
Newham Borough Council said it was concerned about rising levels of racial harassment. Figures for the Metropolitan area covering Newham, Tower Hamlets, Hackney, Havering, Barking and Dagenham showed 419 people were racially assaulted during 1993.