The classic clean-coal power station is reckoned to be only slightly more expensive to build than a coal steam plant, and is cheaper to run that its gas turbine equivalent. Should governments provide a subsidy?

I think governments should provide a subsidy. Everything that can be done to reduce carbon emissions should be done! Maybe the EU should stop subsidising European Farmers etc and start pushing more money into projects like clean-coal.
I also believe that the big energy companies should start showing a real commitment and really pushing green and carbon low energy.
They seem to have bigger and bigger profits but they dont seem to be pushing the issue enough!!! So get going Shell, BP, Exxon etc

Rather than providing a subsidy as an incentive, I am more in favour of having a price on pollution. In a perfect market, all externalities of an economic activity should have been accounted for. Therefore the most viable and rational option will surface. Ideally, markets should function in that manner. If Governments spend their effort to put a price on carbon, that will help the industry to switch out of their current free riding on other people's woes and provide the right incentive for clean coal and other alternative sources energies to be economically viable.

The good thing about putting a price on carbon is that it can be self regulating. If clean coal is not as clean as claim and not as efficient as thought, market forces ought to be able to push that technology out of the market and replace that with the next best alternative. The pitfall of subsidy is that market incentive will get distorted and resources will be required to regulate and monitor the use of the subsidy.

It also mean that base on current level of understanding we have picked our winner. More often than not, once the winner is picked, it is difficult to argue against it and difficult to adopt a competing alternative, especially when significant public money is involved.

I think the Kyoto Protocol is already a proper answer to your suggestion of having a price on pollution. The EU is already fully aldherent to its targets. Unfortunately, the political forces in charge of the USA and China seems not care about the consequences of theirs archaic development's models to the environment of us all. Whatever comes from China don't amaze or surprise us, because they were till recently stuck in poverty. But we couldn't imagine this attitude from the only superpower in the world, USA.

I think governments should develop the correct and full set of rules, that can be the basis for a level playing field. Using more energy requires more generation. This can still be prevented by having the correct measures in place. KYOTO is one. Reducing the effect of the Carbon content of fuels has been / is / will be / very important. Subsidies will not help: there will not be such a thing like global subsidies.....So another attack to not address the basisc: use less energy, assure the generation/conversion of primary fuels follows the most efficient way, including all required parameters entered into the equation.