The Liberal Democrat business secretary launched a robust defence of the Transatlantic Trade and Investment Partnership (TTIP) talks, telling the Huffington Post UK: "It does rather expose one of the weaknesses in their position because if you are a true believer in free trade then you want to trade more with the US."
"It's not clear if you were Britain out on its own how you'd possibly be able to negotiate a transatlantic treaty with the United States. The gateway to the US is actually through the European Union's negotiations."
Cable also warned that the United States would "simply push ahead" with trade talks with Asian economies if TTIP talks fail.
Prime minister David Cameron has praised TTIP, which could be the biggest bilateral trade deal in history, as a "once in a lifetime" opportunity, and recently vowed to nail the "myths" surrounding the negotiations.
The trade deal, supporters say, would create jobs and boost the UK economy by £10 billion a year, but critics - including trade unions - have urged the government to explicitly exempt the NHS from trade talks, fearing that the deal would open up the health service to American private healthcare firms.
Cable said he was "genuinely baffled" by such fears about Britain's health service. "The only sense in which this is in any way relevant is that its design, as in the European single market, is to ensure that procurement is on a non-discriminatory basis," he said. "All that is envisaged for the health service is that principle of non-discrimination is extended."
The cabinet minister played down suggestions by his government colleague, health minister Earl Howe, that it would be "highly unwise and detrimental" to exclude the healthcare sector from TTIP trade talks.
"I think what he's driving at, and some people say it's not relevant why it isn't it explicitly ruled out, the reason is that there are health service providers in the UK who are exporting to the United States who run into 'Buy America' provisions and who want to be able to trade without discrimination."
"It's got nothing to do with allowing the Americans to interfere with our NHS - which is free at the point of use."
In response, Ukip's health spokeswoman Louise Bours MEP told the HuffPostUK: "Mr Cable says it is not about USA interfering with the NHS, but it is interesting that he doesn’t say it couldn’t happen."
"We have listened to the trades unions representing health workers, and agree with them that TTIP is a very grave risk to the NHS."
"Personally I am more inclined to believe health professionals on this issue than the former Chief Economist of a huge multi-national corporation, who is used to putting profit before health."
"We are not anti-free market, but we are anti-NHS privatisation, and TTIP risks widespread privatisation under our very noses. As an independent nation we would be in a much better position to negotiate international trade agreements. Many non-EU countries manage it."
"Of course, Vince Cable might not be able to do it, but that says more about him than it does about the UK. It seems ridiculous to say the NHS needs to be included so that health providers can trade with the US, what exactly is he expecting us to export to the biggest private healthcare providers on the globe?"
Meanwhile, the Unite union renewed its call for the government to explicitly take the NHS off the negotiating table in the TTIP trade talks.
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Len McCluskey, Unite General Secretary, said: “If TTIP presents no threat to our NHS, then why doesn’t the government simply exclude it? This secretive deal will lead to the irreversible sale of our NHS to American corporations.
“Under pressure from a groundswell of opposition, Lord Livingston finally admitted that the NHS is not exempt, but now the government are promising it is safe anyway. When two thirds of polled voters demand that the NHS be excluded, it’s clear nobody is going to be fooled by a promise from a Lib Dem.
“Trade Commissioner Karel de Gucht has made it clear that the door is open for the government to exempt the NHS and now parties across the spectrum support vetoing health. The coalition stands alone."
A poll recently carried out by Survation found that most of those polled (68%) opposed the inclusion of the NHS as part of the deal. Barely one in four (23%) of those planning to vote Conservative supported including the NHS, while 77% of those planning to vote Ukip opposed including it in any TTIP talks.
Syed Kamall, leader of the Conservatives in the European Parliament, has previously poured scorn on the "myths' surrounding the TTIP negotiations.
Blogging on the Huffington Post UK, he wrote: "If the TTIP negotiations cover issues other than trade, it becomes known as a "mixed agreement" and will have to be ratified by the British Parliament.
"Democratic oversight and transparency is a core shared objective of the parties and Members of the European Parliament across the political spectrum are closely monitoring the different stages of the process in order to inform our citizens and to engage them in the process."