How much private sector in NHS?

I tried to set out the arguments for and against increasing the involvement of the private sector in the provision of NHS healthcare, in a short film for the Ten O'Clock News last night.

The central questions for me are these ones:

1) If you accept the argument that a bit of competition from the private and voluntary sector will help to spur productivity gains throughout the NHS (and not everyone does), what is the optimum share of NHS provision that the private sector should provide to deliver this benign outcome (right now, the private and voluntary sectors provide about 5% of NHS healthcare)?

2) Since there is evidence that competition is most effective at raising standards when weaker institutions, unable to raise their game, know that they will go bust, are we happy to see NHS hospitals put out of business? And if we are, can arrangements be put in place to minimise the disruption for patients and communities?

3) At what point (if ever) would the private sector's clout within the NHS be so great that private providers would be able to hold to ransom taxpayers who finance them (pay us more, or else), eroding the productivity gains? As we've seen with the financial crisis at the care home provider Southern Cross, the threat of an interruption of a vital service is quite a bargaining chip for a health provider.

4) And will the greater transparency of costs of different treatments and therapies likely to be brought by increased private sector involvement in the NHS start to undermine political and public support for the principle of universal provision that is free at the point of use? If it does, would that be a good thing or a bad thing?