Michael Gove has attacked the decision to spend more than £9 million of taxpayers' cash on "one-sided propaganda" rather than the NHS after David Cameron insisted it was "money well spent".
The decision to send a Government-produced leaflet to every household in the country setting out the case for voting to remain in the EU in June's referendum has provoked a blistering row between the in and out camps.
Downing Street said the move was a response to polling which showed 85% of the public wanted more information from the Government to help them make an informed choice on June 23.
The Prime Minister said he would "make no apologies" for throwing the full weight of the Government behind one side of the argument, declaring: "It is not, in my view, just legal - I think is it necessary and right.
"I don't want anyone to go to the polls not knowing what the Government thinks, and I think that is money well spent."
But the Justice Secretary - one of four Cabinet ministers campaigning for the "leave" vote on June 23 - said it was "wrong".
"I want a fair campaign, I want to hear from both sides," he told the BBC.
"I just think it is wrong that at a time of austerity, £9 million of taxpayers' money is being spent on a one-sided piece of propaganda.
"That money should be being spent on the NHS and the people's priorities, not on propaganda."
The cost of the promotional push was greater than the £7 million each the formal Leave and Remain camps will be allowed to spend by law in total during the last 10 weeks of the campaign, Vote Leave complained.
Ukip leader Nigel Farage questioned whether the referendum was now still "free and fair".
Speaking at the launch of Ukip's Holyrood election manifesto in Edinburgh, he told the Press Association: "I know that this was a stunt that Harold Wilson pulled back in 1975 but I would have thought one of the very reasons for the establishment of an Electoral Commission was that the ground rules in this referendum were supposed to be free and fair.
"Given that HM Government is not a registered participant in this campaign, I think, frankly, it's outrageous to use £10 million of our money to tell us how we should think and how we should vote."
The PM, addressing young people at a rally in Devon, denied the move was "undemocratic".
"We are not neutral in this. We think it would be a bad decision to leave. We think it would be bad for our economy, bad for jobs, bad for investment, bad for families' finances.
"We think it would be bad for universities. We are not neutral so we have made a clear stance in this leaflet which everyone will get a copy of."
He went on: "There is nothing to stop the Government from setting out its view in advance of the campaign and that's what the government did in 1975, when we last had a referendum.
"I want everyone in the country to know just how strongly the Government, that works on your behalf - you might not agree with everything it does but it works on your behalf - feel that the right choice is to stay in.
"That is why we are spending this money.
"I want everyone to have all the information at their fingertips but I absolutely make no apology for the fact that the Government has a strong view and wants everyone to know that strong view."