Long story short =imported Kramer strat copy US to UK (for a project!!),shipping approx $40.
[ Months later they tell me i must pay Customs duty...not applicable as guitar's total value only worth £85.]
NOTE : Be sure to contact HM Customs and Excise to get a duty rating - if the goods are above a certain value you WILL have to pay.
An electric guitar produces a signal/tiny voltage through the pickups..... and should not receive one .......so you're Aok there....... most fx pedals work on 9to12 volts or so and are usually battery powered
.if you get a UK adaptor for it,as long as the polarity and output voltage is ok then you'll be fine. The only problem I can see is if you get a us adapter and try and use it in the UK (US voltage is about 110 volts,uk about 240v)
Accuracy,you say? hmm interesting concept..