The DOE in 2006 estimated the costs of wind power as around $1 million MW installed on land and $2 million for offshore:
http://www.renewables-advisory-board.org.uk/vBulletin/attachment.php?s=0...

Unfortunately since then costs of many inputs have risen drastically, with steel being notable.
Here are the latest estimates I have seen:
http://www.reuters.com/article/environmentNews/idUSL1483748320080514?fee...

These still do not take account of the latest round of steel price increases AFAIK

From the Government paper it can be seen that the estimated capacity factor for off-shore wind in the UK is around 0.30, so you get a cost per MW of average hourly power generation of around $20million, or £10 million MW.

This does not include many of the costs involved in connecting up the turbines, or back-up capacity.

You can get a very generalised corroboration of these figures from the £100bn bandied around in the press as the estimated cost of the renewables commitment, which is overwhelmingly wind, although it does not include the full projected 33GW installed capacity for off-shore as much of that would not happen until after the time horizon, but does include a lot on cheaper on-shore wind.

Wind is a better resource than is indicated here as it is strongest in the winter when most needed by a factor of two, which helps a lot.
Unfortunately though you can get cold, windless snaps in the winter for several days, which means that additional back-up or transmission is needed, and also relies on natural gas for this, supplies of which are increasingly problematic.

For nuclear costs the highest estimate I have been able to find to date is from EON, who give a figure of up to £4.8 bn for an Areva reactor of 1.6GW:
http://business.timesonline.co.uk/tol/business/industry_sectors/utilitie...
Nuclear reactors will cost twice estimate, says E.ON chief - Times Online

At a capacity figure of 90%, around current US practise that gives you average hourly output of just over 1.4GW (France gets lower capacity factors, but does not run its reactors for maximum output, as not all of it is always required) you come out with a maximum figure of under $7million MW average hourly production.

This would not include all connection figures, as the larger reactors would mean that that would need upgrading, but since they will be sited on existing sites that is by no means as challenging as connections for wind power..
No allowance is made either for cost reductions due to series build.

It is clear then that off-shore wind is around three times as expensive to build as nuclear.

Costings are very different for on-shore wind in the States, which has excellent wind resources, and things like speed of build and ease of finance help bridge any small gap in costings.
That gap is just too big in the case of off-shore wind in the UK for it to be bridged.

It would not be so bad if we were likely to retain our present earnings and ability to finance expensive projects.
As Euan has made clear with his articles, neither is likely to remain true, so in my view the projected build will simply not happen.

This issue has been extensively discussed in the comments to this article on a grand solar plan for the US.
http://www.sciam.com/article.cfm?id=a-solar-grand-plan&page=1

It boils down to nuclear reactors being quite tough targets, and heavily protected.
The containment vessel at Three Mile Island for instance, did its job and prevented major releases - even with terrorist control, which would not last long as members of the special forces would be told to take the kid gloves off, it would be fairly difficult to breach the vessel.

Bowing up a natural gas tanker or poisoning a water supply is by comparison trivially easy, as would pathogen release.