Their claims are based on the latest figures, which show increased revenue from designated Olympics lottery games and broadly decreasing revenue from standard lottery games (see table above).
Money from standard lottery games is divided between the Big Lottery Fund and sports, arts and heritage funders. Between 60 and 70 per cent of BLF funding goes to the voluntary sector, along with varying proportions from other funders.
The Olympics lottery games are designed to raise a total of £750m. They have already raised more than £200m, but few observers believe people are spending this much on top of playing regular lottery games.
It is difficult to calculate the extent of sales diversion, or 'cannibalisation', something which the Department for Culture, Media and Sport expects to be about 5 per cent of sales from regular lottery games.
The Olympics are taking a growing percentage of total funds but the total spent on the lottery might not have been so high without the Olympics lottery games.
Greg Clark, the shadow charities minister, told Third Sector the Government had not upheld its promise. "Now we have evidence that Olympics scratchcards are eating into lottery funding for the original good causes," he said.
Don Foster, Liberal Democrat spokesman on the lottery, said: "Good causes will lose out on more money than previously expected and it could yet rise even further. The impact of such a raid on voluntary groups could be devastating."
A DCMS spokesman said: "It is far too early to say with any accuracy how much of the £750m is likely to come from new Olympics lottery games and how much will come from sales that are diverted from mainstream lottery games."