As part of this process, the Cabinet Office issued draft policy directions in August outlining its plans for the BLF, which are currently out to consultation. The directions say the BLF will distribute funds "primarily" to the voluntary sector.
The Conservative manifesto for last year’s general election said the BLF would "focus purely" on the voluntary sector.
It claimed this would help to ensure that lottery funding to voluntary organisations would increase even though the proportion of funds given to the BLF would fall from 50 per cent to 40 per cent.
The BLF is currently committed to giving at least 80 per cent of funding to voluntary organisations, although the actual figure is 92 per cent.
In his letter to Maude, Sir Stuart Etherington, chief executive of the NCVO, said: "The NCVO believes that 100 per cent of BLF funding should go to the voluntary and community sector, but the use of the word ‘primarily’ in the guidance leaves room for uncertainty.
"It was our understanding following the change in lottery allocations across distributors last year that this would be the case."
The local infrastructure body Navca and the training and advocacy organisation the Directory of Social Change have expressed similar worries about the discrepancy between the directions and the Tory manifesto.
Etherington said that, overall, the NCVO "welcomed a move to less prescriptive guidance" but had other concerns about the directions.
He said social enterprise needed to be better defined "to ensure that money is not diverted away from important projects without a clear understanding of where it is going".
The directions also say the BLF should be used for "strengthening and increasing the capacity of the social investment market".
Etherington said in the letter: "The guidance must ensure that lottery funds are the catalyst for innovative social investment and not the capital of the social investment market".
Consultation on the policy directions ends on Friday.