My friend always tell me that if I wash clothes at night, it would help cut electric bills because according to him electricity is cheaper at this time from 6PM til 6AM.
He is thinking of the Economy 7 tarriff where electricity is very cheap for 7 hours from 11pm to 6am or midnight to 7am depending on BST or not.
It was designed to make it cheaper to use electric storage heaters which heat up overnight.
You need a special 2 rate meter and for the electricity company to bill you accordingly.