Rating Newest Oldest. Best Answer: The average cost for a standard domestic user in UK is about 12.5p per KWh. If you have an economy seven account with storage heaters that heat up at low cost times of the night then you might get away with paying only 6.5p per KWh. Commercial users pay about 1 pence more per Kwh.ating Newest Oldest. Best Answer: The average cost for a standard domestic user in UK is about 12.5p per KWh. If you have an economy seven account with storage heaters that heat up at low cost times of the night then you might get away with paying only 6.5p per KWh. Commercial users pay about 1 pence more per Kwh.