The posts on nationalisation confirmed to me my own views on the role of the state in providing services and which services they should be.  I have to say my own as I am not sure we ever really decided an outcome but to sum up my position:

1) You work out the advantage of the state running the service (i.e. who pays, who misses out under the private sector, will the service be provided at all)

2) and compare that to the cost of intervention (bureaucracy and efficiency)

Some services (typically goods such as cars, pens, suits etc.) are best served by the private sector and others (education, health, law and order and defence) are best provided by the state. 

Looking at this there seems to be a clear split, government seems to be most advantageous when dealing with national infrastructure and the private sector when dealing with private goods.

But energy has me a bit stumped.  It is a private service or national infrastructure?  Perhaps it has elements of both, the private sector can deliver more efficiently but can get out of hand so there is justification for state intervention on prices or profits every so often (or does this arbitrary use of power end up hurting pensioners who own the shares in their pension schemes so it is not that clear cut).

Answering that underlying point may lead us to justify or not a windfall tax (beyond merely saying that we don't think its "fair" that they are making all that money).