In the above paper please note the following additional information to the Acknowledgment section.
The author gratefully acknowledges financial support from the Economic and Social Research Council (grants: RES-586-47-0001, ES/H029745/1 and RES-586-47-0002).
Please also note the correction to table 8.
In table 8 the figures are quoted in January 2010 prices, this is incorrect. The figures refer to 2005 prices.