No it is left on, we have been there until Monday and still had electricity.
BUT, you have to get there early to stand a chance of being able to plug in as electricity is not available for every plot, if you are to the right of the road as you enter you may find that the nearest electricity is some 100 metres away, take a long lead with you (I got fleeced £60) for an extension lead one year as I did not have enough cable. WONT DO THAT AGAIN
If not there by Thursday late I would sugest bribing people with beer, or just plug into someone elses as happened to me last year, I had 3 other people plugged into my electric, I had to unplug 2 as it was bloody dangerous..
This year I have my van with me arriving very late Tuesday evening - so hopefully should not have a problem