Just in case any students or apprentices are reading this thread, I think I should comment on the impression given by "strechyboy" that the supply voltage has changed from 240V to 230V in the UK. The supply industry has actually done nothing physical to reduce the supply voltage from 240V to 230V, it's still 240V open circuit at the terminals of the local supply transformer. What has changed, as part of European harmonisation (Cenelec HD472), the declared nominal voltage has changed from 240v +-6% (between 225.6 and 254.4V) to 230V +10% -6% (between 216.2 and 253V), very little change, just a slightly wider margin at the lower end. This suits the DNO's just fine as it gives them a bigger window of acceptable supply voltage in rural areas, without the associated costs rewinding transformers or tap changing.
Note:- A second round of change in the declared nominal supply voltage (Cenelec HD472-S2) 230V +-10% is pending, it was due on 1/1/2008 but has yet to be implemented in the UK.