You need to ring your current energy supplier. They have access to the1:00 records which are stored on a central records system so it doesn't matter if you have changed suppliers at some point.
This site discusses the times.
http://www.uswitch.co...ides/economy-7/#step6
It says:
" When does Economy 7 start?
If you're wondering when does Economy 7 start, it is usually either 11.00pm to 6.00am, 12.00am to 7.00am or 1.00am to 8.00am. However this can vary according to where you live and your energy supplier.
The time will also change when the clocks go back or forward. Contact your provider to check if you are in any doubt."
In my case it is 00:30- 7:30 in winter