@julieca's assumption is that the Tories would implement something like the old US system (Obama significantly modified the individual market) or private insurance in the UK.
But you can't actually do that. The only reason the US system lasted as long as it did is because most people didn't buy on the individual market. They were on Medicare, Medicaid, or on employer plans, where the premiums are the same for everyone in the company.
There's 3 related pillars of an insurance based system: 1) Mandatory participation; 2) regulated premiums and services; 3) subsidies. Removing any 1 of these 3 will ultimately make it collapse.
If you let people choose whether or not to participate while regulating premiums, healthy people opt out, driving up premiums for those who remain. This can result in what's called a death spiral where only the sickest people remain in the pool. If you do not regulate premiums and services, then you get something like UK private insurance, which works because the NHS does the heavy lifting. This can work in the long term but only if you're prepared to let a lot of people die and the end of funded maternity services--i.e. the health system itself can no longer function. If you don't subsidise the poor, you can't fulfill condition 1.
I don't think the Tories care for the NHS much at all and they're happy to run it down, but the private sector in the UK only works because it has the NHS as a backstop. Privatisation or conversion to an insurance based system is far more difficult than they want to think about.
All systems ration in some way--whether by price or by explicit criteria. The question is how and when.