Cameron said in the speech that if his party wins a mandate it will immediately set about a renegotiation of terms with EU members and put any subsequent deal to the British people in a plebiscite.
Non-eurozone members Denmark and Sweden usually line up with Britain on the single market and desire for EU flexibility.
But Copenhagen and Stockholm were lukewarm.
“I thought it was sad he didn't mention the Union as more than a network," said Sweden's minister for European Affairs, Birgitta Ohlsson, adding: “The EU is not a loose network. It's a union with clear game rules.”
“We have no intentions of following Cameron in that direction [to a referendum]. It's in Denmark's interests to have as close ties as possible to the centre of Europe,” said Nicolai Wammen, the Danish minister for European Affairs.
“Denmark has strong alliances with a number of EU countries such as Germany, France, Sweden and the Netherlands. So we will not change our EU direction if the Brits choose to leave the EU,” Wammen said.
Wammen’s last statement would have raised eyebrows in Downing Street, if it was noticed amidst the growing pile of negative missives.
In the Netherlands, a traditional British ally, Foreign Affairs Minister Frans Timmermans, agreed with Cameron that the EU needed to be reformed, saying the Single Market and free trade should be promoted.
"But you only reform the EU from within, not by running away from it," Timmermans said, adding: "The [Dutch] government does not want opt-out clauses and neither seeks a redefinition of the relationship with the European Union."
France offers UK a red-carpeted exit
French Foreign Minister Laurent Fabius quipped with the UK prime minister’s jibe last year that Britain would “roll out the red carpet” for French business emigrating to avoid President François Hollande’s high taxes.
“The other day I was in a meeting with British businessmen and I said: ‘Listen, if Great Britain decides to leave Europe, we will roll out the red carpet for you,’ ” Fabius said.
French President François Hollande was more measured but equally dismissive: "What I'll say, on behalf of France and as a European, is that it isn't possible to bargain over Europe to hold this referendum," the French President said on a trip to the Alpine city of Grenoble.
"Europe must be taken as it is. We can help it evolve tomorrow, but we can't offer to reduce it or diminish it on the grounds of (Britain) staying in it."
More soothing words came from Germany, with Foreign Minister Guido Westerwelle saying his country wanted Britain to remain a full and constructive member of the EU. “We share a common destiny in these challenging times of globalisation, we as Europeans are all in the same boat.”
But he also voiced concern that if Britain tries to cherry-pick EU legislation, it will cause other countries to join in and result in unraveling of rules.
Swedes do not like cherrypicking
“Flexibility sounds fine, but if you open up to a 28-speed Europe, at the end of the day there is no Europe at all. Just a mess,” echoed Carl Bildt, the Swedish foreign minister.
French Finance Minister Pierre Moscovici was one of the rare, relatively positive voices, saying Britain had always been a “particular” but “extremely useful” member of the EU.
Another crucial relatively supportive message came from German Chancellor Angela Merkel. “Germany, and I personally, want Britain to be an important part and an active member of the European Union,” said Europe’s most powerful politician.
“We are prepared to talk about British wishes, but we must always bear in mind that other countries have different wishes and we must find a fair compromise. We will talk intensively with Britain about its individual ideas but that has some time over the months ahead,” Merkel added. Germany’s support would be vital if Cameron’s referendum ever materialises.
On the domestic political front, both the opposition Labour Party and Cameron’s coalition partners, the Liberal Democrats, were united against the referendum gambit.
The genie is out
In Britain, Cameron's speech also met with a deluge of criticism.
“Why doesn't he admit it? He's been driven to it, not by the national interest, but he's been dragged to it by his party,” said Labour leader Ed Miliband, adding: “My position is: 'No, we don't want an in/out referendum.'”
Miliband claimed Cameron was taking “a huge gamble with our economy”.
Cameron’s deputy prime minister, Liberal Democrat leader Nick Clegg, said: "In my view it's not in the national interest"
"My view is that years and years of uncertainty because of a protracted, ill-defined renegotiation of our place in Europe is not in the national interest because it hits growth and jobs," Clegg said.
Perhaps more ominously for Cameron, Nigel Farage, the leader of the United Kingdom Independence Party – which campaigns for the UK to leave the EU – said: “The genie is out of the bottle.” Farage accused Cameron of being a phoney eurosceptic.