The attack came as the Chancellor personally unveiled a £9 million blitz by M&C Saatchi for the Inland Revenue and the Treasury to promote the new child tax credit, which takes effect next April.
The first phase of the campaign broke on TV this week with an ad showing which families would benefit, against a backdrop of sterling notes.
Urging them to claim, the voiceover said: "If you've earned it, make sure you claim it, because it is money with your name on it."
Early next month, a second TV ad will encourage people on existing tax credits to claim the new benefit. A third burst in late October will highlight case studies showing how much typical families can receive. Similar ads will run in the press and on radio.
But David Willetts, the Tory spokesman on work and pensions, issued figures showing that in the first two years of the working families tax credit, the Government spent more than £20 million on advertising but achieved a take-up of only 62 per cent. He added that a £3 million push to promote the minimum income guarantee for pensioners had 840,000 responses, but resulted in only 82,000 extra claims.
"Labour's past advertising campaigns have been both costly and ineffective," Willetts said. "Frankly, it doesn't matter how much the Chancellor spends advertising his latest tax credit. They are so complicated that tens of thousands of eligible families aren't collecting the funds."