Liberal Democrat leader Nick Clegg has criticised Chancellor Alistair Darling's first Budget for being a "cop out" on green issues.
He also said the government would get "nowhere near" meeting its child poverty targets.
Mr Clegg claimed increases to winter fuel allowances for the elderly were one-offs and accused Mr Darling of "playing with" people's hopes.
The chancellor had "over-egged" any "good news", he added.
In his speech to the Commons, Mr Clegg ridiculed the government's claim that this was a "green" Budget.
He said Mr Darling was using environmental taxes - such as reforms to vehicle exercise duty to penalise the highest polluters - to take more from "the kitty of the lowest earners".
He also described Mr Darling's plan to impose charges on non-domiciled workers who remain in the UK for more than seven years as a "flea bite".
Mr Clegg said Prime Minister Gordon Brown, himself chancellor until last year, was driving economic policy, calling the Budget an "act of political ventriloquism".
He told MPs: "This was an opportunity to give whatever help possible to the millions of hard-pressed families who are feeling the pinch, whose money is simply not stretching as far as it once did.
"But that's not the Budget that the chancellor has delivered.
"This is a meagre, tinkering Budget which gives precious little help to the poor but maintains special treatment to the rich - a Budget designed to fill a black hole masquerading as good for the environment.
"A Budget which will not make Britain fairer. A Budget that is a green cop out."