The B.C. Liberal government's new "prosperity fund" is effectively financed by Medical Services Plan fees, not the natural gas windfall promised by Premier Christy Clark three years ago, say opposition MLAs.

In her response to the B.C. budget Tuesday, NDP finance critic Carole James said relief from MSP fees for lower-income families doesn't take effect until January 2017, along with another four per cent overall rate increase. A new $100 million "fantasy fund" is raised through MSP revenue and other fee increases rising this year, James said.

Changes introduced by Finance Minister Mike de Jong will exempt children from MSP rate calculations, and raise the qualifying income for the full rate from $30,000 to $42,000 for single people. That single adult rate rises to $78 a month starting next January, the latest of a series of increases for Canada's only dedicated medical service fees.

Green Party leader Andrew Weaver said the MSP changes are a "halfway step" in the right direction.

"We see individuals and families earning modest incomes continuing the pay the same rates as those who are earning six-digit salaries, and assistance remains contingent on an opt-in system," Weaver said.

James said contrary to de Jong's description of a nation-leading provincial economy, B.C.'s private sector job growth is sixth among provinces and average consumer debt is $10,000 higher than the national average.

"We see people leaning on payday loans and credit cards to try to pay their bills," James said.