Tory chances at the next election could be severely dented if David Cameron fails to block a marketeers’ charter from entrenching NHS privatisation.

A new poll revealed yesterday that a whopping 68 per cent of voters surveyed in 13 key Tory-held battlegrounds want the Prime Minister to seek an exemption for the NHS in the controversial Transatlantic Trade and Investment Partnership (TTIP).

And if he fails to secure this, 54 per cent want out of the treaty altogether — and would call on Britain to exercise its right of veto.

The poll — carried out by Survation for trade union Unite — shows an astonishing 9 per cent swing to Labour in the constituencies, threatening the wafer-thin majorities of lawmakers such as Thurrock’s Jackie Doyle-Price and Amber Valley’s Nigel Mills.

The agreement pledges to “harmonise” US and European Union regulations — meaning Britain would open the floodgates to greedy multinational health privateers.

Labour shadow health secretary Andy Burnham has raised concerns over the treaty’s implications in meetings with EU bureaucrats.

Unite general secretary Len McCluskey said: “The Tories’ Health Act of 2012 opened our NHS up to profit-making US private firms and a new trade deal threatens to make the sell-off permanent. It’s clear from this poll that the NHS is going to be a major issue at next year’s election.

“We don’t believe the empty promises coming from the bureaucrats in Brussels, but Cameron could act today and protect our health service. David Cameron’s silence is deafening.

“Unless he acts the NHS will be at the mercy of US companies and Wall Street investors who will be able to sue the government in secret courts if it tries to reverse privatisation.”

Survation chief executive Damian Lyons Lowe said: “When the potential implication of this trade deal are put to voters, they are clear that protecting the NHS is of paramount importance, notwithstanding the benefits of a trading partnership.

“Should public awareness become widespread, this could, based on our polling, become an electoral liability for David Cameron if he does not heed public concerns.”

A Department of Health spokesman said they had “no intention of allowing the TTIP to dictate the opening up of NHS services to further competition.”