Kitumbula Mazambi, his wife Mapendo Kasiba and his brother Kyalemaninwa Mazambi were convicted at Isleworth Crown Court yesterday of conspiracy to defraud.
A statement released by the Metropolitan Police said that between 2001 and 2005 the group had set up a number of charitable bodies, some of which are believed to have been registered with the Charity Commission.
They applied for funds of up to £60,000 a time for "projects that were so vague and nebulous that it would be extremely difficult to check whether the projects had in fact been carried out".
The statement said the group had done some charitable work, but had spent a large proportion of the money on "volunteer expenses", stationery, petrol and administration costs.
"The vast majority of paperwork that police uncovered could not be verified, had little or no audit trail and involved fraudulent invoices," the statement added.
"In summary, there was little or no evidence of bona fide charitable work being done, but ample evidence of the suspects using the funds to finance their lifestyles and/or send abroad."
The police said the three had also sold their "fraud expertise" to others for what it describes as "substantial sums of cash". They were part of a cell of nine people who together defrauded charities of more than £1m. The other six members of the cell have already been convicted of fraud and are serving a combined prison sentence of more than 17 years.
The group was caught in August 2004 when a grants officer at a predecessor of the Big Lottery Fund noticed suspicious similarities between a number of grant applications. The organisation alerted the Metropolitan Police.
A joint statement issued on behalf of the Big Lottery Fund, Comic Relief and Children in Need said: "This determined group of criminals operated a sophisticated web of deception targeted on defrauding UK funders of charities at the expense of the public who provide these funds.
"When their activities were uncovered, rigorous steps were taken to isolate early any potential multiple applications as a result of their activities. Additional controls have been put in place to prevent any future attempts to defraud funders."
A BLF spokeswoman said the fraud took place under its predecessor bodies, the New Opportunties Fund and the Community Fund, before they were merged to form the BLF in 2006.The three will appear at Isleworth Crown Court for pre-sentence reports on 17 September.